Have uploaded a Zip file with 2 Experimental bin files, 1 is just CartConv on Linux the Other File
is a rebuild of the Cartridge.
I have no way to test so might not work at all.
I see that 64 CUPCAKECART uses .prg files,
so if you download the Prg files from here:
https://thereaperuk.itch.io/reapers-mega-cartridge-image-c64
The "TheC64Maxi-Mini Prg Files.zip" download option, you will find Sub-X Prg file in the Zip, So try to use that with the Cupcake board.