I saw a post mentioning car door lock solenoids that will pull a bolt one direction when one button is pushed, and pull it the other direction when a different one is pushed.
You'd have either a two-way momentary switch, or two different buttons, one for lockdown, one for release.
Everything would have to line up nicely. those solenoids would have to go right into the holes smooth as butter, the first time, or they'd end up sitting on the outside of their holes and your CP would slide off when you let go.
EDIT: I bet you can get car door lock solenoids cheap as Ramen at the local junkyard. (Ramen being cheaper than dirt)