Hmmm... I don't think it was implemented in the original version. There was a hardcoded zoom function but I didn't even remap the keys
I'll have a look-see if anything can be done -- with a minimum acceptable amount of hassle, that is.

Meanwhile try replacing the game executable with this file (copy it to /opt/mog/ and chmod +x it, you know the drill). Now the up/down cursor keys should control the zoom level which should alleviate your problem.... somewhat.