I'm trying to do it at the moment. Was told there is no quick way, I have to apply as normal, just like everyone else. If you are above the BMI value though, you can get a letter from your unit to say when you last passed a PFT and CFT. if you haven't passed one in years, then your going to have to get fit like the rest of the applicants. (I'm way over the BMI personally, but got said letter).