I just discovered your mahjong game... I love mahjong games ;)
Maybe you can just clone the X key on fire 2 on joypad to make it fully playable on GX4000 ? It would be the only mah-jong game on this system :o)
And a restart key ("p" key ideally to make it available on the pause button on GX4000) would be great too in case you are in a deadlock situation.