Are you using the 47RH transmission from a 95?
I so, you could semi automatically control the OD and TC without the PCM but it would not be perfect. (of course, neither is the PCM)
There is an electronic speedometer module available that can be used to trigger relays to operate the OD and then the TC in sequence when a set speed is reached and to disable them both below that speed.
The so called "mystery switch" would still be needed for optional control.
I am putting together a relay box that will do that for my 94 but it's purpose is to override the PCM until I'm ready for it to do it's thing.
Basically it is to prevent OD or TC operation until the set speed is reached then control is turned over to the PCM.
In your case, you would still have to monitor and manually control the TC and OD while they were in operation.