I don't know of any "clear" spray-on stuff, but I've used this "Spray-on protection bra" from Griot's Garage on the wife's BMW when we take it on long trips and it works like a charm.
www.griotsgarage.com/search.jsp?searchtext=20264 This is a "temporary" bra and is excellent for use during trips (like driving to Ohio for the London show!). Neat thing about this stuff is, once the trip is over, you simply peel it off.
I have the Invinca Shield on the Cobra and it's great. It has saved me a lot of $$$ on paint! I will say however, a section of mine started to yellow (even though it's guaranteed not to). I called them about it and they sent me the front sections at no charge............but I'm too chicken to take the old section off (I've heard horror stories about paint peeling off with it!). So far, I'm content to live with it the way it is since you only notice it if you're really looking for it (and you only see it where the white stripes are - not the blue sections of the car), but if it gets any worse, I may have to heat it up and give it a try.
Has anyone here had any success getting this stuff to come off?