With the second controller built, I connected it to the tentacle last night and gave it a whirl. It worked!

It looks like I'm going to need a rigid mounting fixture to prevent the base from twisting. I also had to be very particular with the arrangement of the cable housings (extension spring in this case) such that they don't cinch or rub against each other while the tentacle moves. With the proper base fixture, I can probably solve both of these issues to make mounting a snap.