At weekends the airfield is used by 618 Volunteer Gliding Squadron -
http://www.618vgs.org.uk/. Contact details are on there. I'm not sure if you could get PPR via Ops for an out-of-hours use if the VGS were prepared to look after you, but it's worth a try, especially if you arrive during 'open' hours so they can process your paperwork on arrival. (Try to avoid being parked on the south side... it's a long walk!)
Sadly Odiham has no RAFFCA club or I'd point you that way instead.
You will need to pay the landing fee plus insurance unless you have the annual waiver from HQ STC at Wycombe.
Tim