Cruise control mod for fixed throttle position

[Zerfstead]

Here is an idea I would like to try.
I drive a 2006 Scion xA with auto trans and a factory cruise control. When the cruise is engaged, the speed varies + and - 2 mph while going over a freeway overpass and makes (I think) too aggressive and output. I have been watching the TPS number on the ScanG II. I think I can add a switch to open the power to the servo motor in the cruise module and the result would fix the throttle position at the set value. Then I have a speed control that operates in the normal cruise mode and in throttle set mode.
On a long trip, set the cruise at 50mph and then switch to fixed mode to lock the throttle position. The SGII should show changes in grade and wind conditions.