I have done a couple with kydex. I just made a mounting bracket out of kydex that bolted onto the sheath rivets that the belt loop of the leatherman case rode on.
I have also made a few leather combo sheaths that used the same idea. Just made a jumper that bolted to the sheath that the belt loop from another sheath could ride on. It would be just as easy to put a leatherman on these instead of a piggyback knife.
Good luck,
Todd