I have had success with UE3, using a Junction Point to relocate data that engine is looking for to another location. Basically, install this
and then move your Unreal Project directory wherever you want it to go, then as it says on page for that utility you can set new location as target, and drop a Junction Point back into your original location. As far as engine is concerned files are still where it wants them, but they’re actually being stored elsewhere.
Its still a dirty hack, but it doesn’t affect other aspects of your environment.