Ok, so here is what I do:
I insert the mechanical stamp and link the visibility of it to a yes/no Instance parameter called Mechanical
I do the same for Electrical, but call the Yes/No parameter Electrical
Then to save on some time, I create two family types, one for Mechanical & Plumbing, one for Electrical with the appropriate visibility set for each.
By doing this I am able to control the title blocks per sheet and I don't have to mess with it later on.
When setting up the project I try to setup more sheets than I think are going to be used for each discipline, that way people can just delete the sheets they don't need and don't have to worry about trying to set them up correctly.