Noob here, first post - a great site!
Handthrottle:
Perhaps a little cross pollenation: jeepers use hand throttles a lot offroad and it's a simple mod, probably adaptable to most cars. Here's an
installation.
Many simply get the parts from a bike shop. Goes unsaid that you have to be a bit careful using it.
CC Hack:
One of the jeep guys hacked the steering wheel
CC controls to run the winch in and out and control engine RPM in steady state (to charge the rapidly depleting battery). It has a switch to go back to 'normal' use. It's not the same as what you're building, but it may poke some thoughts.