i dont think its possible yet, although it might be on magnetiks to do list.
ive got a work around though, download and install powerstrip. you can set it up to automatically change resolutions when you launch programs. i had it set up to automatically disable my second monitor when GTA3 was started, because GTA3 is incompatible with muiltiple monitors. then when you exit the game, it automatically turns the second monitor back on.
get it here: