Why can't you just disable the 4,000 rpm rev limiter, by fooling the computer? It can only know that the clutch is not engaged, by the clutch switch, so just tape or fix the clutch switch in the closed position and the computer will always think the clutch is engaged, which should take care of the rev limiter. The only other thing the clutch switch controls is the starter disable, when the clutch is not depressed, so you will just have to remember not to start the car when the clutch is up, because if the car is in gear it will leap forward.