Yeah, assuming the emulator uses the same macros from libogc (WPAD_BUTTON_LEFT, WPAD_BUTTON_RIGHT, and so on) for the filelist controls, this should be easy.
EDIT: Well, it took a while, but I *think* I did it. The emulator uses an "input port handler" (src/emu/inptport.h) that works by using its own constants and giving them values that correspond with those used in libogc to handle the controller input. Of course, this works by generically using the same constant names with every type of controller; this reduces greatly the amount of code used (and yes, I was expecting this from the beginning).
I don't really know if it will work properly or not - again, I don't have any MAME ROMs
. Give it a try and tell me:
https://dl.dropboxusercontent.com/u/6957349/powerpc-eabi-mamemini_high-limit+filelist-mod.rar. It still has the 10000 files limit.