Actually, I just stumbled across MAYA_MODULE_PATH which does pretty much what I need.
I am going with a setup in which we define the following environment variables on each user's machine...
MAYA_MODULE_PATH = source controlled directory
MAYA_SCRIPT_PATH = source controlled directory
The module path allows me to add plugs, scripts, icons, etc in a very organized way and do selective loading should I so choose without having to modify each users env vars.
I had to use the script path because we have a a couple scripts with the same name as out-of-the-box scripts which add to the base functionality of standard UIs. Since module script paths have a lower search priority than default script paths, I have to use this env var to be able to override the out-of-the-box scripts.
Thanks for the input everyone. If you aren't familiar with module setup, you should realy look into it. It seems to be a great way to organize a directory of scripts and tools without the need to constant maintain paths in env vars.
--JeffD