I like the Jag centrecaps too. In fact, I'd run them in preference to the Volvo ones. :)
I cant even fit centre caps (unless I make something up) to my Koya wheels.
There's a half-head height (say that 10x fast) bolt that I've seen in M12x1.75 w/17mm hex head. Let me see if I can find some details on it. Looks like you only need 3-4mm of clearance anyway.
