The handle material is polypropylene and is more than likely injection molded to the knife. That being said I would use a hot knife or a soldering iron with replaceable cutting head, and cut straight down the spine of the handle. You might be able to figure out where the steel of the knife stops in the handle by using a small magnet. Just make sure you do the cutting of that polypropylene outside or with good ventilation. Good luck with the project and remember to post pics.
TBRA