Shoot, that was easy! Thank you QT, X-cart is a sweet baby that just does whatever you tell it to.
See the floating cart in action here:
http://trainingpen.com/home.php?cat=105
If you can't divine the code from what I have already posted, I am going to wrap this one up as a module, even though it is dead simple, it is quite useful IMO.
PM me if you are interested in beta testing.