In the RAF it is not enough to want to do something and having the requisite skills and ability. There has to be a need. If it is not in the Service Interest for you to change branches then you will not. Also consider not only will the pilot branch have to have a need for your services, but the WSO branch will also have to be happy with being one down.
Since the age window for pilot training is so narrow, it would appear that chances of crossover would be minimal. I have always advised people attending OASC that they should not accept a branch, if they are not prepared to be employed in that branch.
Nevertheless, circumstances change. For those reaching an exit, prospects for employment in the civil sector are good. On the grapevine, I suspect that more pilots will leave than the RAF are anticipating and therefore there may indeed be a need.
At Lyneham I know of 3 ex Navs, 1 ex Air Eng and 2 ex ALMs who are employed as pilots.
Good luck.