Building iso using mock/pungi but replace one rpm - how?

[mike cloaked]

I build my own Fedora DVD install isos - and currently I have a need
to build an F15 DVD install isp using the latest version of the lorax
rpm that is in updates testing, but not yet in stable.

Does anyone know how to run a pungi build based on a standard
development/f15 mirror repo, but to use a specific replacement rpm in
the build - in this case getting the lorax rpm from updates testing
but to use all the other rpms from the stable development/f15 repo?

Alternatively if you have an iso is there any way to replace the lorax
package within that iso with a newer version by somehow loop mounting
the iso and then repacking it with the newer rpm?

Thanks

-- 
mike c