You could go to controller options and select the next value up for number of stations. Create a new station and set it to RF, then add it to your program using the master or pump station. When OS turns on the dummy RF station the master will come on. As far as i know OS has no way to know if it is successfully communicating with an RF station so it should just “send” signals off into oblivion whether or not the station exists.
Of course all that is only possible if you have not actually used all 48 available station slots. The only reason I post this when you specifically stated you have no free slots is because most assume you can only use the number of stations matching the physical number of slots. If you have indeed used all 48, then there is no way to schedule the master on it’s own, without setting it to a normal concurrent station and overlapping its run times with your individual station run times.
I hope this helps