This has been (if not still is) possible, although luck and sheer determination would appear to play a role. I'm personally aware of one who failed initial pilot selection, joined as firefighter (with no real intention of fighting fires, but keen to get in), re-applied and eventually went on to earn his wings. Another who initially joined as engineer and was later put forward for pilot selection due to both his service record (and presumably alot of ass kissing) and simply being in the right place at the right time. Lucky boy!
Tho as other have said, certainly go direct if you can.