In an attempt to win a argument (with my chief instructor at the time) I developed a spreadsheet where you can input a groundspeed, and a rate of descent and it will tell you the angle you're moving down.
If the math is right a constant 30kts groundspeed with a 500'/min r.o.d. should yield a 9.46 deg. angle, keeping 30 kts., and increasing r.o.d to 800'/min should give a 15 deg. angle. (Interestingly, 1700'/min at 60 kts groundspeed gives a an angle if 15.8, so a typical r22 auto should demonstrate a textbook steep approach angle)
Of course we don't fly approaches at these constant conditions, but you could set up a steady state descent holding these numbers to demonstrate an angle to a student.
The best solution if you really wanted to fly and visualize precision glideslopes would be to build an alignment of elements visual glideslopt as mentioned in 2-1-2 e. in the
AIM You could make it adjustable to demonstrate different angles!
I think students should be taught to fly apporaches with a lot of variation, i.e. slow and shallow, fast and shallow, slow and steep, etc.. as this develops a great feel for the ship which can then make flying a "normal" approach a no brainer.