It is a bit of hack but might work. If you need a code example and are using JS have a look at the following thread:
http://smartbear.com/forums/forum/post/?mode=singleThread&thread=80d933b1-8266-4c98-b4cc-64f29b196a08BTW, In regards to your Source Control, adding and removing variables would most definitely change their project files, but (depending on your SCM) you could either hijack the files temporarily for the run, work on an exported copy of the files, or even check out and in through scripts before and after making changes to the project file.
Still not a great solution though :-(
