Description of problem:
machines using a local user session network (like Boxes) will not preserve the dhcp lease and its IP address will change on each reboot.

network xml file does not allow any lease time definition whereas dnsmasq allows you to set the expiry time next to the network range

There is no documented way to do this at least, and by looking at the code I haven't found any way to get the xml file to generate the right dnsmasq configuration.