So I got sort of impatient waiting for a Gamebit screwdriver. I was already sort of miffed that the iFixit kit I wanted was sold out here atm so the only obvious solution was: I'll do it myself then.
Tried one that was available here but the outer diameter was too big for GBC cartridges so I made my own, that also has a handle. Some tweaking later and it actually sort of worked.

NOTE: This isn't really a good design per se, my current PLA filament (Easyprint gray) is quite soft so I had to compromise. While it does work for GBC cartridges, it does also wear out the teeth a little each time you use it because you need to jam it in place a little. However I figured I'd still upload it because, well, it does work in a pinch and I really wanted to see if it could be done at all, and if the teeth do get all messed up you can do the "lighter trick" people do with pens on youtube and it should work again for a while.

Doesn't Matter

No

0.2

100% walls

I edited a photo of a gamebit seen from the front and traced it, but as that one was made of metal I slightly redesigned the teeth a little to better suit PLA.