I can recommend the maclock bracket. Not inexpensive (on sale for $60 at the moment) but mounts and looks fairly clean, all things considered. I don't like the "shell" version and the less expensive hinge locks have me worried about possible damage.
Maclocks made a nice move here since they offer 3 different solutions for the MBP-R:
1- The security case and lock bundle- I got this one when they launched it, I actually love how the case elevates the MBP and protects it, I took the rubberized black case that is actually strong and hardly being scratched.
They have 13" version and 15" version. Also have a combo lock version for both sizes which is cool!
3- For people who don't like a case on their MBP-R they made the locking bracket which integrates the security slot within the MBP-R by attaching the bracket underneath using the MBP-R's original 4 screws, I have checked with both an Apple store specialist and Maclocks rep. it doesn't harm any warranty. I actually thinking of buying this one only because it is made of a steel (though the rubberized case is a pretty strong polymer).