Independant run up mode has throttle hold (at the programmed idle point).

It is possible to do what you are asking but there would not be enough demand to justify building it.

However I do have a new product I am working on that will do what you are asking. It is a governor/limiter. It is really for Helis or potentially extreme airplanes. You can select governor mode or limiter mode. In governor mode it holds the RPM at a defined RPM set with an Aux channel. In limiter mode it lets you control the throttle normally but will not let a preset RPM be exceeded.

There is one other option as well. I have a four engine sync unit that is basically two twinsyncs combined (one for inboard and one for outboard). One is master and sends the target RPM to the slave via the aux port. The slave would do what you are asking for you will just need a way to send it a signal (i.e. a master with a user interface)... It will be expensive though unless we build a few hundred. I think the governor/limiter is a better option.

Bill