The pointing crypt keeper is powered with a PIG 2 and it's mounted on a micro servo. "Hard to do" is kind of relative. I did have to cut the production plastic. I also had to make custom servo mounts using some thin sheet metal.
I'm sure there are other ways to accomplish this. This was really meant as a one off mod and I'm not sure how I'd make it a kit. I'll happily answer any questions if you want to take this on yourself.
The clearances are VERY tight. If it's too far forward you start having to worry about the glass and the ramp. If it's too far back, you can snag a foot on the tombstone when it raises. I actually made that mistake and had to pull it all apart (after these pictures) cut the plastic more and move the servo forward about 1/4 inch.
I normally opt for fully reversible mods, but it just wasn't possible here. And, why would you ever reverse such a cool mod?
Also, that servo is not visible from the front of the game. It's pretty hard to see from the sides.