It is possible to go straight from check-in into The "Airside Services" Department (formerly known as Traffic).
There are a few people who have gone straight from being a PSA to a TCO.
Just shown an interest in the department, ask to go and shadow as them much as you can - not just when the job vacancies go out like most others do.
You will normally have to do at least 18 months out on check-in before you can make the move tho.
Good luck.
