I haven't done it myself, but here's how I'd probably go about it:
1) start with a complex mixer
2) mixer 1: src=thr, define a curve which is 0 at -100 and ~15 at 100
3) mixer 2: src=rud, define a cuve which is 100 at -100 and 0 at 100. Set the type to 'mult'
4) mixer 3: src=rud, 1:1, type = add
That should provide throttle compensation as throttle is increased with a reduced factor as rudder is applied and becomes dominant.
If you have a devo10, you could use one of the knobs to control the scale factor To do that:
in step (2) above set the curve to go from 0 to 100, define a new mixer between (2) and (3) as:
src = Aux4, curve: -100: 0, 100 = 100, type = mult
