So I've come up with my own solution. I changed /opt/retropie/config/scummvm/emulators.cfg default entry to point to a custom launcher script of my own:
#!/bin/bash
game="$1"
pushd "/home/pi/RetroPie/roms/scummvm" >/dev/null
/opt/retropie/emulators/scummvm/bin/scummvm --fullscreen --joystick=0 --extrapath="/opt/retropie/emulators/scummvm/extra" -p "/home/pi/RetroPie/roms/scummvm/$game.svm" --auto-detect
popd >/dev/null
And then I just make sure the scummvm rom directories end in ".svm". This custom script utilizes the --auto-detect flag so that scummvm figures out what game it is. So far in my testing it works.
Obviously this launcher script could use some work, but it's doing the job so far.