I went through the games I wanted to to include on the cab, and came up with this configuration which allows 90% of them, and is both intuitive and comfortable:
B A R
Z C-dn C-lf
It tested really well for Mariokart which was the priority (powerslides are intuitive, and I use my thumb for 'item') but also works for Starfox64, Mario Party, Super Smash Bros, Diddy Kong racing, Beetle Adventure Racing, Mario Tennis, Bomberman 64, Mario 64, some others.
Since my player 3 and 4 only have 4 buttons, their layout is
B A
Z R
They lose brakes and turbos in Starfox, and handbrake in beetle racing but Kart, Smash Bros, Tennis and Party are unaffected at least (and all players lose camera buttons sometimes. No biggie though)
Untested on Sin and Punishment, Worms and Ocarina (Losing Ocarina kills me, but I doubt I'd stand in front of a cab for hours.) Maybe I can get away with not having a top C and right C) I knew I'd lose 007 after 2 mins of testing with a digital stick.
Anyhow, until game-specific configs are released or hacked (ZSNES does this no problem) I highly recommend this set-up. What do you guys use?