Hi
Try the driver commands "Set Selected Signal State v4" kuid2:368725:60002:4 or "Set Signal Ahead v2" kuid2:368725:60003:2 both by Elstoko and on the DLS. The first one allows you to set any named signal while the second one allows you to set the next signal ahead to the state required.
When the old Auran built in colour light signals are used these commands cause the calling on lights to light while the main light remains red. It may be that with a semaphore the animation doesn't work but these commands may still allow the loco to pass.
With the first command, once the loco has passed the signal and coupled to its train, reissue the command again to reset the signal to automatic.
Not all signals will work with the commands so it can be a matter of trial and error to find ones that will.
If you need to see an example of the first one being used then I have a session for the ECML on the DLS (its the only thing I have on there so just search for my username) which makes use of the first command. It uses mainly built in content with just a few bits and pieces from the DLS.
Regards
Brian