Added v2 which has a thicker base with more overhang preventing it from sliding over keyboard. Works better. I should delete the originals, but putting our revisionist quest to perfection on display seems to be the maker way.

http://www.friday.com/bbum/2013/06/22/bluetooth-keyboard-caps/

These caps can be placed on an Apple Bluetooth Keyboard to cover the power button and prevent it from being turned on when floating about your backpack.

Pick either style and print 2, mirroring one to print the piece for the other end.

Or just print one and take it off when you use the keyboard such that it remains level.