You can always heat up the insert in the oven and form it to the blade.

300 degrees until it's soft and then press it between two pieces of carpet foam with the knife in it.

Wrap the blade in two layers of masking tape for clearance.

The screw at the bottom of the sheath will get the insert out.

Don't apply to much pressure when you press it.

Pretty sure Rainwalker could make you a Kydex insert for it as well.