Mupen64plus key stop mapping to a number

[enjmab_ment]

Hey everyone! First time poster, amateur retropie/raspberry pi hobbyist.

I think I've figured out the problem I ran into, but don't know that there's a way around it.
In the standalone Mupen64plus emulator, I want to map the Kbd Mapping Stop value to a number 0-9, but the default "select savestate slot" seems to take priority over that. I've got a 2-player arcade setup that uses an I-PAC2, and I've got the buttons mapped alright and both work well enough for games that require only a few inputs (mariokart). But all of the 'menu' keys are numbers, and I want to be able to enter and leave all emulators without needing to plug in a keyboard.

/opt/retropie/configs/n64/mupen64plus.cfg

SDL keysym for stopping the emulator
Kbd Mapping Stop = 27

Using this list of SDL values: http://www.libsdl.org/release/SDL-1.2.15/include/SDL_keysym.h
If I wanted my input "3", I should just need to put 51 there. But that doesn't work.
Just about every other value I enter there does though, so I think I'm close.

I couldn't find anything in the config file or the Mupen64plus wiki or this other wiki or this one that would remove or change the savestate stuff.

A workaround I thought of was trying a key combination, but they don't seem to work the same way the joypads do: button(J0B9/B3), etc. The below should be Backspace+Return to exit:

Kbd Mapping Stop = key(8/13)

Anyway, I'm at a loss here and wanted to see if anyone else has tried something different or gotten around this. I'd honestly rather not have savestates and be able to exit the emulator using my usual hotkey command ("3"+"1"); key(51/49).

I feel like I'm reading all the right wikis, but I'm coming up short somewhere. Any help is appreciated! A flat "you can't" is good too, if it means I can stop running down this rabbit hole.

Thanks!