I installed my game (and all packs and ep's) on my D drive, then all the custom in my documents on my C drive, and it works just fine.
Yeeeeeah, but the problem I have is that I don't have the space on my C:\ drive for CC, so I would need to place the on another drive, but I don't know if there is a way to tell the game where I've installed them.
EDIT:: Right, I think I might have found a solution. I didn't know you could tell Windows where you want the Documents folder to be - I knew you could go and create one, but you can tell Windows where it is and it will move everything over there, and that will be the new, official Documents folder.
I just did this, then tried loading up Fallout: New Vegas, whose save files were auto-moved into the new Documents folder, and it found the save files fine. Also, I saved and the save file went into the new Documents folder.
I cannot test the Sims 3 yet, but hopefully now the folder is 'official' it shouldn't be a problem.