Oh good grief. 'Airframe parachutes' or 'lightweight ejection seats'. While no doubt well meaning you are rather demonstrating why the RAF has such trouble with all this.
If the darn thing is so hard to get out of, make it easier. Why was that not part of the original assessment - or was it?
So - sort its exit procedures. Improve the canopy jettison if required. Add air bags under the seat squab - becoming common practice in heavily reclined position racing sailplanes. Use a time expired airframe or simple mock-up to allow passengers to practice exit before flight if you are really paranoid. There are relatively cheap effective solutions.
The AEFs and others used Chipmunks for years, with standard parachutes for cadets. That was viewed as satisfactory, with adequate briefing. What has changed - the attitude to risk ?I flew a Grob 109B occasionally. Really hard to get out of quickly, but it can be done. We carried parachutes. Handy to practice exits, just in case, if high enough.
But there will always be risk.
This is not directly part of the Air Cadets thread it seems to me, though the OTT thinking at time sounds rather familiar!