You are right that if you're on the Fast Track escalator then when you get to the upper floor you may well be penned into a busy pair of channels with no easy escape. You should just ask the HAL agent at the top of the escalator to allow you to go slow track, I have never been refused.

Better still, take the lift instead of the escalator, then when you get to the security hall you can decide whether to reclaim Fast Track status or go with the flow. The lift exit is slightly set back from the queue lines.