I Think the idea of panter can work if we modify it:
What about leaving off the signal of the fast track?
It won’t matter, because the route trains take on a line is absolutely fixed at a line level. If you open the lines dialog and take a look at the routes highlighted on the track, those are the routes the trains will take no matter what. If the line ahead of a train is utterly deadlocked it will not take an available alternative path if the line definition says it needs to go through the deadlock.