ge_mapchooser_resthreshold 100
should do the trick. However, ge_transition is essential for preventing client crashes when switching between two maps that use a lot of memory. We found during development of 5.0 that for whatever reason during the switch to the new map clients can get overloaded with assets from both maps and crash, necessitating the use of a blank map in-between them in an attempt to flush the buffer before loading the new map.
It should be fairly straightforward to preserve the nextmap settings if the current map name is "ge_transition". Just check the map name before applying them, and if it happens to be "ge_transition" simply prepare to apply them to the next map instead. There are a few features in the code that do this and there seems to be no issues with it. You can disable it for testing of course, but if it's at all possible I'd recommend finding a way to keep it on.
Regardless, I can't wait to see your finished product! Sounds like it could be useful.