Well, that's exactly what happened - and other people on this thread have verified they did the same. There were lots of people, but you could walk without stopping virtually all the way to the platform. When the ref blew up, I left my seat in ESU (so had to negotiate the stairs). then fast walk...
Erm, I left on the final whistle, walked straight onto the platform and caught the 1701 to Lewes. The queues are nowhere near as bad as they used to be.