If you're that tight for space, re-install the game on the drive with extra space, and then copy over all your settings folders, film files, etc to the newly-reinstalled directory.
You cannot separate the directory where AH saves film files (not yet -- it has been requested before, though. Maybe they will listen)
EDIT: Space-saving measure: 1) clear out unwanted film files -- these can add up if you don't review them, 2) check screenshots -- if you have thousands try zipping them or deleting the crap ones, 3) every AH update that the game downloads puts a patch .EXE file in your root AH directory and once the patch is installed you can delete the install file (Just don't delete the one named AcesHigh.exe! I've done that before by accident), 4) Custom skins, if you have them all downloaded and installed, probably take up over a gigabyte (if not 2GB) of space -- feel free to delete some!