I had a thought on modifying a planer like that too. I usually work on a mule setup. I was planning on setting up tracks on either side of the timber. I would make them out of straight lumber. I would have cut out the middle of the base and put rollers on the bottom of the two sides to assist in its travel. The timber could then be shimmed on the corners to make it stable if it has a little twist.

Now that I have the makita 12 inch, I will probably attempt the same rail system. But, I will use blocks clamped on either side of the planer. I should only need to shim the front of the planer so I just might make rollers that attach to the same screws that the front handle is attached to. With the beam shimmed to the right height, This should plane out any twists or crowns.