I was thinking the other day...they could, if they wanted, bring the master in this series without explaining the backstory; the Doctor simply wouldn't recognise him.
You could have Actor X (I actually think Tony Head would make a good, albeit very different, master) playing a character in an Episode...at the end, after the doctor leaves, or while the Doctor is elsewhere, said character pulls appropriately enigmatic expression, then steps into his own TARDIS and disappears.
Enough to leave the audience wondering, and then setting up expectation when he returns later / the following season.
Just a thought...
VB