Just give all the MCV s Prerequisite=FACTORY, every building TechLevel=1 and comment out Required/Forbidden Houses. Although MCV owners are only one side (as listed) I was able to get other MCVs this way.
Or simply change all the prerequisites to generic TECH/FACTORY/POWER/PROC. That way you'll get all factions' buildings at once. Although I don't see a point in that.
Why would you do that? It's not only unnecessary but it also messes up the order in which the sidebar icons appear. They are displayed by tech level, low tech first and high tech last.
But I'm sure it's possible. Just follow the instructions of the others that posted so far.