Remapping keyboard on C64 core?

I want to play with the C64 core, but I have an ordinary PC keyboard plugged into the MiSTer, and it is incredibly hard to find the right keys for things like the double quote.

Is there some obscure file I can write to remap the keyboard just for the C64 core?

I don't necessarily want to change the global MiSTer keymap because I also want to use other computer cores, and switching the keymap back and forth is going to get old quickly.