If you're current wheels is at +1, and you want them to be -12, you'd need 13 mm of offset which is roughly 1/2". Unfortunately that's probably not something you'll be able to do.
It will be too thick to safely do with slip on spacer because that will be leaving you with only 1/4" of thread engagement. That will fail, it's a matter of if not when.
It will be too thin for a bolt spacer because the stock lug studs will contact the face of the wheel. The studs being roughly 1.5" will stick out 1" beyond the face of a 1/2" spacer. That's too far for even a stock wheel, but they can use a spacer that is slightly thinner than 1.5" because they have pockets between the holes which allow the stud to fit. If your Fuel wheels don't have that pocket you'd have cut or replace the stock studs, and even with that it's a bad idea. As noted a few posts ago you want roughly 1/2" minimum thread engagement (that goes for the spacer too) so a 1/2" spacer wouldn't have room to counterbore for the nuts holding it on.
Basically, the thinnest bolt on spacer you'll find will probably be 1".
So you've got 4 options.
Push them out about 1/4" with a 6mm slip on spacer.
Push them out about 1.5" with a bolt on spacer.
Leave it as you have it
Buy new wheels.