Best thing at the current time is not try to use the idle on that throttle. It's the worst throttle design I've ever seen. Use a throttle stop to get it to have a good idle between high and low idle rpms, and use ignition idle advance to dial it in.
That said, I've been working this week on trying some ideas for hardware to control that throttle. All concept so far and hope to start trying some things on the bench by the end of the week.