Have you considered 3-D printing your mold? Not sure if that would work, I've been tossing around the idea of molding some grips as well and thought of the 3-d printing.
Can you post a link to the video Derek was making?
Custom build done for a street vendor in Miami Fl. The bike started life as an HBBC SkullXBones. It was stripped and custom painted, along with the Wheels and Hubs. Built back up with the springer and ape hangers. Trailer is completely custom, built by American Vintage Camper in Marysville...