Self Build?
One way forward might be to encourage cadet organisations to look at self build projects to get more youngsters engaged in aviation. Rather than bus a bunch of cadets to an AEF or VGS in the hope of a flight subject to weather and aircraft some bases should have a self build project underway for cadets to assist with.
For example, RAF Cosford has an AEF, VGS, Cadet HQ, gliding club, Joint Service Flying Club as well as being the home of RAF Engineering. I think it could also be a place for a self build project where, under supervision, cadets are shown how a basic glider or powered aeroplane is built. Cadets can then have a go at riveting, metal bashing and other trades before being allowed to do something live on the self build kit.
Once completed to the satisfaction of the LAA, BGA etc the self build aeroplane could be handed over to the club for use.
Sadly, the MOD is so risk averse they would wet themselves at the thought of teenagers building a glider or powered light aeroplane. When I was 17 there were still schools bungee launching kids in primary gliders from playing fields and as far as I know there were few serious incidents with these hops.