I bought some 18" high polished factory wheels off of a 2008 CTS to put on my 2005 CTS. It appears the center of the 08 wheels is not big enough to clear the rotor assembly on my 05 car. Has anyone found an adapter to make this set up work

I sincerely doubt this is possible.
The lug studs are a different size on the '08 and nothing will be properly centered.
You will end up with vibrations (even if you can get them on) and possibly worse.