There is a pilot at Brize who was posted to a ground tour and asked if they could leave the RAF and join the aircrew reserves (part time) to stay flying.
The Sqn has to agree to the requirement for the 'slot', which it did. The person was full time one day and in the reserves the next as its apparently easier to administrate that way - maybe it's an aircrew or part time reserves thing? This info was first hand from the OC of the reserve Sqn so fairly confident it's true in that persons case.
It's a great deal for the RAF as its a cheap option for them, no pension, just a days pay with a min of 27 and max of 90 a year. The person stays flying in a job they love.