Combining drills?

[Streetboat]

I have a question: how on earth did Frictional games make the script for combining the drill in Storage? Right now, I have a puzzle wherein the player has to look for the parts for a drill, but there's a slight twist thrown in: there are two drills, and one is a red herring. One is a smaller, plastic toy drill, and then there's the real one. I want to make it possible to combine the appropriate three parts together for each drill. The toy drill and the real drill can be combined separately, but the toy drill has no real use. Is this possible? I looked all over the 12_storage hps file, and found absolutely nothing about the actual combination process, except for a GlobalVarInt called "DrillParts" that adds up to 3.