I love the game and I play it on my c64 mini and now on C64 Ultimate FPGA. But why can't you just jump with the button is beyond me. I cannot recommend this game because up to jump while the button is unused makes the game painful to play. Otherwise it is a fantastic game, but only playable on an emulator with remapping the up to a button.
Hmm, GMod2 support (this is the cartridge format) might be a little cumbersome on the Ultimate (got the latest firmware?) - it seems it does not load the settings. Please hold M while starting the CRT. It will open up a menu with settings where you can chose tojump via button. To save the settings permanently, you need to save the cartridge changes within the Ultimate. With a physical cartridge all of this works out of the box - just as it does on ViCE - also on the Ultimate. It is the Ultimate's emulation for GMod2 cartridges that is a little tricky to use.