I created a bootable USB stick with the F17 beta RC2 x86_64 DVD using:
livecd-iso-to-disk --format --reset-mbr /path/to/iso /path/to/usb

When I install using that disk and select "custom partitioning" both the local hard disk and the bootable USB stick are selected and the USB stick is the default target for the bootloader. If I use any of the other options ("use all space" etc.), the USB stick is not selected as the default target for the bootloader.