I wanted to be able to build livecd images for both i386 and x86_64 on an x86_64 machine, and couldn't figure out an easy way to do it (without running livecd-tools from a chroot), so I came up with the following patch that allows specifying --basearch=i386 on the command line, overriding the detected value.
Created attachment 304658 [details] Patch adding --basearch command line argument
Just use setarch(8) setarch i386 livecd-creator ....
Ah. I RTFS'ed and saw it first checking /etc/rpm/platform, but I didn't realize that /etc/rpm/platform doesn't actually exist on x86_64.