I've verified that the patches are adequate to perform the task Simo is requesting, and they've been ACKed upstream.

Dan's patch has been pushed upstream:

commit 6510c97bf5920044355d22646a91fb0a8fb9bf68
Author: Daniel P. Berrange <berrange>
Date:   Mon May 28 15:04:31 2012 +0100

    Add some missing hook functions
    
    A core use case of the hook scripts is to be able to do things
    to a guest's network configuration. It is possible to hook into
    the 'start' operation for a QEMU guest which runs just before
    the guest is started. The TAP devices will exist at this point,
    but the QEMU process will not. It can be desirable to have a
    'started' hook too, which runs once QEMU has started.
    
    If libvirtd is restarted it will re-populate firewall rules,
    but there is no QEMU hook to trigger for existing domains.
    This is solved with a 'reconnect' hook.
    
    Finally, if attaching to an external QEMU process there needs
    to be an 'attach' hook script.
    
    This all also applies to the LXC driver
    
    * docs/hooks.html.in: Document new operations
    * src/util/hooks.c, src/util/hooks.c: Add 'started', 'reconnect'
      and 'attach' operations for QEMU. Add 'prepare', 'started',
      'release' and 'reconnect' operations for LXC
    * src/lxc/lxc_driver.c: Add hooks for 'prepare', 'started',
      'release' and 'reconnect' operations
    * src/qemu/qemu_process.c: Add hooks for 'started', 'reconnect'
      and 'reconnect' operations

pkgs:
libvirt-0.9.13-3.el6.x86_64
qemu-kvm-rhev-0.12.1.2-2.297.el6_3.x86_64
kernel-2.6.32-280.el6.x86_64

Prepare a domain
# virsh list --all
 Id    Name                           State
----------------------------------------------------
 -     rhel6u2                        shut off

Prepare a script
# cat /etc/libvirt/hooks/qemu
#! /bin/bash
echo "$0" "$@" >> /tmp/qemu.log
exit 0

Add x mod
# chmod +x /etc/libvirt/hooks/qemu

steps:
1. start the domain
# virsh start rhel6u2
Domain rhel6u2 started

check in log:
# cat /tmp/qemu.log
/etc/libvirt/hooks/qemu rhel6u2 prepare begin -
/etc/libvirt/hooks/qemu rhel6u2 start begin -
/etc/libvirt/hooks/qemu rhel6u2 started begin -

2. restart libvirtd
# service libvirtd restart
Stopping libvirtd daemon:                                  [  OK  ]
Starting libvirtd daemon:                                  [  OK  ]

check in log:
...
/etc/libvirt/hooks/qemu rhel6u2 reconnect begin -

3. destroy domain
# virsh destroy rhel6u2
Domain rhel6u2 destroyed

check in log:
...
/etc/libvirt/hooks/qemu rhel6u2 stopped end -
/etc/libvirt/hooks/qemu rhel6u2 release end -

4. attach domain
# qemu-img create /var/lib/libvirt/images/foo.img 1G
Formatting '/var/lib/libvirt/images/foo.img', fmt=raw size=1073741824 

# /usr/libexec/qemu-kvm -cdrom /var/lib/libvirt/images/foo.img -monitor unix:/tmp/demo,server,nowait -name foo -uuid cece4f9f-dff0-575d-0e8e-01fe380f12ea  &
[1] 1688

# virsh qemu-attach 1688
Domain foo attached to pid 1688

# virsh list --all
 Id    Name                           State
----------------------------------------------------
 2     foo                            running
 -     rhel6u2                        shut off

# cat /tmp/qemu.log 
...
/etc/libvirt/hooks/qemu foo attach begin -


5. lxc hooks

Now define lxc domain get this error:
# virsh define xml1
error: Failed to define domain from xml1
error: internal error unexpected domain type lxc, expecting one of these: qemu, kqemu, kvm, xen

So this is bacially blocked.

> 
> 5. lxc hooks
> 
> Now define lxc domain get this error:
> # virsh define xml1
> error: Failed to define domain from xml1
> error: internal error unexpected domain type lxc, expecting one of these:
> qemu, kqemu, kvm, xen
> 
> So this is bacially blocked.

Make a mistake here, define should be:
# virsh -c lxc:/// define xml1
Domain toy defined from xml1

# cat /etc/libvirt/hooks/lxc
#! /bin/bash
echo "$0" "$@" >> /tmp/lxc.log
exit 0


# virsh -c lxc:/// start toy
error: Failed to start domain toy
error: internal error guest failed to start: PATH=/bin:/sbin TERM=linux container=lxc-libvirt container_uuid=d1f4798b-bebf-d93c-1d97-fe1c1cb7c780 LIBVIRT_LXC_UUID=d1f4798b-bebf-d93c-1d97-fe1c1cb7c780 LIBVIRT_LXC_NAME=toy /bin/sh
2012-07-25 07:38:51.688+0000: 1: info : libvirt version: 0.9.13, package: 3.el6 (Red Hat, Inc. <http://bugzilla.redhat.com/bugzilla>, 2012-07-20-03:24:32, x86-010.build.bos.redhat.com)
2012-07-25 07:38:51.688+0000: 1: error : lxcContainerIdentifyCGroups:1282 : Unable to read directory /sys/fs/cgroup: No such file or directory
2012-07-25 07:38:51.691+0000: 6548: info : libvirt version: 0.9.13, package: 3.el6 (Red Hat, Inc. <http://bugzilla.redhat.com/bugzilla>, 2012-07-20-03:24:32, x86-010.build.bos.redhat.com)
2012-07-25 07:38:51.691+0000: 6548: error : virCommandWait:2314 : internal error Child process (ip link set veth1 netns 6549) status unexpected: exit status 2

^^Another bug is filed to track this:
https://bugzilla.redhat.com/show_bug.cgi?id=842979

check the log:
# cat /tmp/lxc.log 
/etc/libvirt/hooks/lxc toy prepare begin -
/etc/libvirt/hooks/lxc toy start begin -
/etc/libvirt/hooks/lxc toy stopped end -
/etc/libvirt/hooks/lxc toy release end -

Eventhough domain fail to start, but the hook is working as expected.
So, this is fixed.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2013-0276.html