I read the following on the MAMEDEV.org-FAQs:
"To save the state of a game, use the default save state sequence of Shift + F7. At this point, you will get a prompt asking you to select a slot. Type a letter from 'a' to 'z' and the game's state will be saved.
...
To restore a saved state, use the default load state key F7. Again, you will prompted to select a slot to load from, and the state will be loaded."
So maybe i can assign another button as a substitute for a letter on the keyboard?