Not sure if this has been mentioned already but don't the army take regular soldiers etc (who admitedly are keen/good at fitness/sport), "train" them as PTIs and then return them to front-line service and effectively be PTIs as a secondary duty? I'm sure I'll be corrected if I'm wrong.
On my last sqn we looked at trying to get a couple of our groundcrew trained in providing fitness classes etc (on the HAS site so we didn't all have to troop to the gym - a lengthy trip when your the wrong side of the airfield or when PTI support was unavaialbale (end of a night shift)) but the opposition we got from certain areas, well known for wearing singlets, was incredible. Before you ask they had to be "formally" trained to comply with H&S and insurance regulations!