OK, I am thinking a two piece sheath, fully enclosed blade up to the 4th rivet up from the bottom, or maybe the 5th one (just so it will not jump out of the sheath. OPEN SPINE up to maybe the last rivet before you get to the handle molding where there should be some kind of retention strap perhaps from the edge side, around the back and snap on the front side on the edge side to keep it from rocking out of the sheath. IF you needed added retention you could always run some paracord through one of the rivets up and around the finger guard side and secure it with a knot or a spring loaded cord "Tie"

I'll try a crude windows paint picture of what I mean.