Would these spacers be feasible?
 

http://www.ezaccessory.com/Wheel_Ada.../4100-4100.htm

I've never dealt with this type of spacer; bolting the spacer to the disc and then bolting the wheel to the spacer. I ask because I might be able to pick up a few sets of 265 wide 16" slicks soon, and I know they're too wide for my R56 as it is now. 1" of space should cover it. My only concern is the wheel arch rubbing when I eventually get coilovers and slam it.

I don't have any experience with them personally, but I know that H&R Springs makes them. Check out their website for more details.

I seem to remember people using them with success.

Yes they will work, but your are better off with wheels that are the correct offset.