This is a slightly modified version of the splicer by MaleBuffy to allow using a drill and pinning the teeth. It's still a work in progress as I have new belt coming and will be printing and testing it soon.
This was designed to allow using tiny drills like the kind used for nozzle cleaning or pcb holes. These are very cheap on ebay (as nozzle cleaner) for a set of 10.
This re-mix adds two changes. A small 3mm guide hole centered to a tooth such that two belts can be placed and drilled without as much risk of drill breaks and to keep alignment. I think this is repeated for 2-3 teeth. There is also an opposite 0.5mm hole so that a "pin" can be inserted from the other end and tapped into the hole. Most likely this won't print well but can be drilled out to accept pins smoothly. I've yet to figure quite how to remove after pin insertion but probably the belt can be lifted enough and the pin clipped. We'll see.
The other change is to add a couple slots to the end to allow accurate belt "three way" cuts. Place one belt in and cut twice, repeat for the other belt, and then remove opposite portions so they can fit each other. Then move to drill position for final steps.
There's some videos on Youtube of doing a drilled/pinned splice. They're not great but get the idea across. It's probably going to be a lot easier with a jig like this.
Once I get the belt and print this and try I'll report back on how well it works and how well the final joint holds. I expect to glue the back as well so this should just add to durability. Will add a few photos of steps/process too.