Acutally david, i think p-g-qvm supports that too. I think it is the syntax of /callvote map layout.
But re-reading his post, i got another impression of what he meant. He meant a way to make a layout load by default, or even specify a new default layout.
I have added a new issue to the p-g-qvm issue tracker, for a new cvar g_defaultLayout added to the mapconfigs for each map. Lets you change the default layout of a map.
This might not be possible, however, i am not sure.