Mister Bonkers
MB,
I agree your technique for Ex 4 will be absolutely fine. You can always demonstrate difference between Gov On and Off on the ground at full ERPM/RRPM. Nothing to prevent that in the manual and I have always found doing so before getting airborne reassures me that the student understands the finesse required. Better than having their first go in flight when over controlling can lead to an interesting time.
My experience is that at Ex 4, most students are bombarded with so much information that they don't fully appreciate the role of the governor anyway and are much better placed to understand its operation pre-solo with a good few hours under the belt.
Only problem I see is the demonstration of effects of disc loading and airspeed on RPM. The student will get little out of a demonstration with Gov on. I assume that the CAA expect these specific requirements of the syllabus AMC 1 FCL.210.H (d) (v) (B) to be covered under the Emergency procedures as well. A bit of guidance wouldn't go amiss.