An experiment:
Try and start from a known power setting for approach that results in the aircraft settling around the target approach speed. If the runway is long enough, perhaps have a target speed that is a certain amount above the chosen minimum approach speed(say ten knots). That way, if the speed is a few knots below the target, there is no need to adjust power as it is still above the minimum. Not sure if the instructor will like that but it could allow for less power changes required to always be exactly on speed. A justification could be that you want to be further away from a situation where a lot of power is required when inevitably getting slow due to turbulence. Does the airspeed really have to be exact on approach with frequent power changes to keep it there when it could be within a 5 or 10 knot range that is not too fast and not too slow with few power changes and less trimming.
Let us know if it works.