Bought a motocross throttle cable kit off of E-bay
Pulled out original inner cable
Modified the bracket (located to offside slightly forward of the rear wheels) so that the new sheath would slide thru it and refitted it.
BEFORE & AFTER
The outer sheath VW originally fitted has a very large bore, you can leave it in place and slide the new sheath inside it, saving loads of hassle. cut the new sheath to length.
I Turned a copy of the GTi end nipple out of brass and crimped it onto the cable, I thought this made sense as you can re-use the spring clip which locks the cable end into the throttle lever. (Any machine shop should be able to do this, it took me less than an hour.)
Fitted the old GTi outer sheath end fittings onto the new sheath then fitted the new cable and cut it to length then fitted it to the pedal.
You have to clamp the new sheath to the bodywork somewhere in the engine bay.
Chad