There is a problem with this approach, keyboard layouts are different between countries and GameGripper uses a pair of problematic keys. I don't know if you can simply code it selecting position (or number) of the key.

In my case (spanish keyboard) the schematic is something like that:

w t u p
a d l ç
x b m .

So I would define it as:
Up: w
Left: a
Right: d
Down: x
Fire 1: l
Fire 2: p
Fire 3: . (Left in US Englis)
Fire 4: ç (Down in US English)
Fire 5: b
Fire 6: m
Coin: u
Start: t

But for Fighting games, for example I may change configuration so I can have Fire 1, 2, 4 and 5 in the right side and 3 and 6 (strong kick/punch) in the middle buttons.

A trick used in several games/emulators is to change keyboard layout to US English at the beginning of the execution and return to normal state when closing.