I'm not a chemist. I was wondering if we could add instant coffee to xtol or another non-staining developer of choice to make it a caffenol-blend.

I mixed up some coffee with developer the other day to try an 8x10 in. After I turned out the lights, I accidentally slipped the 8x10 sheet of film into the fixer instead of the prewash water. End of that opportunity.

I'm not sure what 35mm film the OP is using, but I think 35mm tmy2 works great with PMK without being grainy.