Any way to make FFWD behave as a toggle?

[TheManuel]

I posted this question to EmuChat but I'm trying to expand my net here.

Is there a setting to make MAME's FFWD functionality work as a toggle instead of having to hold down the button, without recompiling the code?
If only achievable by recompiling, could somebody give me some pointers as to how to do this in the code?

Notice that I'm referring to FFWD not throttle, which doesn't work when you use triplebuffer or any sync method.

Thanks.