I've been trying to figure out how to use my apple wireless keyboard with my rMBP in clamshell mode, connected to my iMac with thunderbolt. It seems like I have to go out and buy a second keyboard in order to do this, but... surely that can't be right. Can it? Doesn't seem to make much sense that I have to buy a second keyboard just to tell the iMac to go into Target display mode. Am I missing something?