Integrated revoshofter broken
 

A friend's 8spd Shimano Revoshifter is broken. It is the type with a pulley cable operated by the grip shift that rotates the gear cable rotating drum thing. The broken bit is a white plastic cog-like bit under the rubber grip that produces the click stops.
I would ditch the whole revoshifter and fit a thumb shifter, but the part is integrated into some perfectly good brake levers (v brake).
Replacements are about £50 which is a lot for an old bike.
Can you replace the gear shifter only on the unit, or cut the gear mechanism away using brute force?
Any low-cost suggestions welcome.

FYI, I disassembled and removed all the shifter elements from the brake housing. I used a Dremel and file to cut the housing back to the size of a normal brake housing, then clamped a used non-integrated 7-speed Shimano Revoshift to the bars.
It all works well now.