What if you had a strap/chain at the front of the seat that secures the cyclic back against the seat, and a "remove before flight" flag connected to the locking device that is long enough to hang in the window? The locking device could then be a combination lock device to avoid the lost keys thing.
Please forgive me if this idea has obvious flaws, I'm good with full size simulators but don't have much time in actual aircraft.
I just love the whole "security" thing.

The wide-eyed panic about this stuff coming from government is almost comical when you consider the relative threat posed by a small aircraft as opposed to, say, a HUGE TRUCK that could get driven right to the base of a building.
But we'll not win that particular argument. It's like where I work full time - they have a physically isolated computer network inside the building for a select group of staff who work on secret squirrel stuff. These people have two computers at their desk, one for the "secure" system, one for the "insecure" system - a waste of resources and a pain to support.
It was suggested that they use a system that the Defence Force uses to protect their systems, removing the need to have a physically separate network. The Person In Charge asked "Is there ANY chance that this system could be compromised by a cracker?" Of course the answer is "well, yes, there is a miniscule, infintessimal chance that this system could be cracked".
The response? "Well, we can't take that chance". No matter that it's good enough to protect our top secret government data, it's not good enough for us.