Drugstore,
I solved the heavy lock tension/pressure on the Griffin by bending the metal strip to the best compromise angles* that still let me pass it through under the screen, but enable the lock to rest out horizontally on the table (instead of being Freudianly upright). With the weight of the lock lying flat on the table for support, the flat flap of the strip lies pretty flat on the MBR, so closing the lid is no problem. I also put a couple of layers of electrical tape or film on the flap to soften the edges even more to reduced the risk of scratches further.
*(curved for insertion,then flatened the last 0.5 inch or so where the lock is, with the curve lessened a little as it nears the lock hole flat part and with a minimal angle bend right at before that flat part for the lock hole.)
Of course that doesn't work when I use a lift under the MBR15 which raises up the back. (I'm very fond of my http://www.aviiq.com/collections/laptop-stands/products/portable-quick-stand as long as the table isn't too slippery for my MBR to not slide). So I'd have to remove the Aviiq if I closed the laptop.
The Maclocks case looks like it would greatly reduce heat removal by convection, and the underside of my MBR does get warm. And plastic seems easy to break, although a strip of metal like the Griffin/PNY isn't exactly real hard to cut or maybe even bend to remove either.
The stongest solution seemed the Laptop Lock Adapter:
http://www.snakechicago.com/
It doesn't take a lot of space behind the MBR, but this puts the lock on the right side in the way of where I'd use my small traveling-use Logitech mouse, and it means I can't use the ports it locks itself into. This would have been good for me if the lock were on the left instead of on the right (though that'd be fine for a lefty), but maybe if I saw it in real life I'd find it's far enough back or doesn't protrude enough to not get in the way? I'm always skeptical. I use a Targus ACH119US 4-port USB3.0 hub when I need more ports anyway and don't really need the SD card slot, so I wouldn't mind sacrificing those to the lock when I need to lock up.
If small size is the priority and you don't mind appying this to your MBR, I liked how clean and small this solution looked (although I'd guess it can be removed with some effort, too, since it's just a strong glue):
http://www.noblelocks.com/wedge/RetinaPlate.html
P.S. -- It looks like Griffin no longer makes its TechSafe Cable Lock. They've removed it from their web site. It used to be at http://www.griffintechnology.com/products/techsafe-cable-lock , so I guess they gave up on the product instead of trying to improve it and sold it to PNY?