This was long time ago, but I'm still interested in the answer...
I've tried Regen, Kega Fusion, Gens, FB Alpha, higan, Mednafen and RetroArch emulators and I didn't find any option or hotkey to speed up the framerate.
With Regen I can slow down the speed, but just that.
It's interesting to see that NES, SNES and Game Boy emulators do have that option to increase FPS in a different alternatives like +10%, +20%, +30%...
But maybe Genesis /Mega Drive has some problem and that's why any emulator has the option...