Missing route - T482 to T1308

Good evening,

While in the testing of a timetable I've mostly finished writing for Three Bridges, I've noticed that it is not possible to set the route past Redhill platform 0 for freight trains to continue onto the shunt signal T1308 to avoid blocking out the South end of the station. The only way that I seem to be able to get trains routed there is to set the route onto the mainline and when the loco runs round it clears. I've seen this done in real life to hold a freight service which is late running however I unfortunately don't have reference.

This is in the 2019 era of the sim.

Thank you in advance.