Sorry Sky Sports - not quite true.
Whilst there may be annoying hoops to jump through (H&S, DBS, ACO orders etc etc etc) a number of units are teaming up as you suggest, and I know of quite a few more currently being looked at.
It might be difficult to get approval, but the ACO is most certainly not "flatly refusing to even consider" as you suggest.
If you do have access to/connection with an ATC Sqn, then they can find the exact procedure in ACTO (Air Cadet Trainng Order) #35.
Not an easy procedure to be sure - but not impossible.
This may be the case, but the 'end user' or 'customer' (14 year old boys who just want to fly) are not being told this. All they know is, they can't fly gliders, while army cadets are.
I am told Gliders are now ready to fly from a technical point of view and the final paperwork issues are now being delt with before release for test flight.
Can we start a sweepstake on how long the 'final paperwork issues' will take to sort out, and at what cost.
I'll start with 1 year and £1M!