From a non-WAFU standpoint, do not even think that you could re-cat easily. Used to be a lie told to young rating recruits at the AFCO that they could easily transfer once they joined up, little did they know. If you want pilot, lose the weight and apply later.
Please correct me if I'm getting a gash dit here, but a good friend of mine who recently graduated said most of the University Air Squadron guys she knew who went on to fly went into the RN as the RAF didn't have any places to offer.