There have been a couple of keychain versions as I recall, someone on Deskthority had a key testing set that included a buckling spring tester. Plus there is this one of mine...

It has a piece of the membrane cloth, and the base of the switch is made from a piece of the baseplate, primarily to try keep the sound authentic. I guess if one piece of membrane was cut out (3 thicknesses) then it could perhaps be a functional switch. For now its just for reasonably accurate sound and feel.
edit: Basically, cropping a discrete switch out of a Model M is possible, but yes it was a bit of messing around. I reckon it could be possible to make the switch functional, again with more messing. I wouldn't like to make a stack of them to build into a new board though.