As the pins of my cartridge sensor were FUBAR I decided to install a permanent "hack". I took a cartridge chip from a new cartridge and hard-wired it to the Cube's mainboard with a switch in the middle. When I need to print I switch it on so the Cube detects a cartridge, while printing I can switch it off to prevent the counter from writing to the chip and allowing me to print bulk fillament. Be careful not to fry the chip, it can not handle heat that well. I managed to overheat the first chip soldering the wires.
For those interested: the cartridge chip: