Hmm, good plan with the extenders. I didn't think they would fit but they should. I checked and, which I did not have a ruler handy, I could fit a SX32 cartridge in preciously. Usb memory for scale.
http://Www.grandis.nu/images/cd32_space.jpg
These should do. 20mm depth without the strain relief.
https://www.elfa.se/elfa3~en_EU/elfa...2-54&toc=19301
and the other side
https://www.elfa.se/elfa3~en_EU/elfa...2-50&toc=19301
Edit: Never mind. I only have 15mm to spare and the smallest one I can find is 20mm. I'll keep looking.
Edit2: Or wait. 20mm is the whole length. Should work.