Sounds strange that your getting this vibration from the clutch pedel, I had a OS twin plate in my 180sx and it was noisy as when you pushed the clutch in. But i never had any vibration coming from the pedel pushed in or out even when it was shagged after some hard launches @ the drags with slicks on.
Just a random stab in the dark but you may have one of these problems
clutch is miss aligned
hot spots on cluthc/flywheel
weak slave cylinder
cracked or busted gearbox mount
cracked or busted engine mount
Clutch Chatter:
Clutch chatter, a vibration and/or noise when engaging the clutch, is likely to be caused by an internal clutch problem. A warped disc, hotspots on the flywheel or pressure plate surfaces, worn or dry input shaft splines, or worn release bearing.