I know this is kinda wheel related, but I have a set of those spincaps:

http://www.spincaps.com

On my CLS, & 1 of them is frozen sold on the valve stem. So much so it broke both keys that came with them to take them off. Thank God it was the last one, & 1 of the little holes the key fits in totaly stripped out. Any ideas on how to get it off? Without damage to the wheel, or valve stem.

 

Call the company and scream. Tell them you want to know how to get it off, and if not they need to pay to have a tire shop do that work for you.

 

I hate those spincap things. I bought two sets of them and they both leak air something terrible.
I complained to the company via several E-Mails & phone calls and they refused to refund my money because it was after the return period.

As for getting yours off, maybe a pair of vice-grips ???
If you grip it at the very end it might mash the inner & outer rings together enough to spin.
Hopefully doing so without damaging the valve stem.

Also, did you try spraying it down with WD-40 or something similar?

 

If what Shawn says doesn't work, drill a hole into the center of it and use a screw remover to get it out.