I think of moves Ryback/Reeves has done, I would think that the Delayed Gourdbuster is pretty analogous to the Jackhammer, though I'm sure the smarks would shit all over that.
I'm rather partial to the Tilt-a-whirl powerslam.
I mean, I can't think of anyone off the top of my head that has used it as often as Ryback, it looks like it's fairly painful, and it may be easier to pull off than his current Shell Shocked move. The only problem is, could he hit the 'spin' on bigger guys? Perhaps it could just be a quicker 'out of nowhere' finisher for putting away smaller guys?
Another notable mention is the Gorilla Press Powerslam, while it would be impressive to lift a guy like Tensei over his head, i'd figure that to be impossible and dangerous to both participants if something went wrong.
Spinning Sidewalk Slam might be easier than the 'Tilt-a-whirl Powerslam' and it has a lot of energy and impact to it. I think he could even pull it on larger opponents and maintain some feel of impressiveness.