Hate to bump a horribly old thread but I'm curious if anyone tried the SPST switch method that Z posted above. If MAME would recognize joystick_map for keyboard controls, it would not be necessary (tested through a key to joy hack). The joystick_map when using 8 way joysticks works very well for 4 way emulation. Until they support keyboards, the SPST method is probably the next best thing IMHO.
-Mc