I wouldn't be so sure.
There's an interview on DS where they speak to Tovey about Being Human and his appearance in DW. It contains this tantalising little bit...
Is there a chance for you to reprise that role again after this?
"Surely. Yes. Sorry, I'm not allowed to say anything!"
Really? Not allowed to say? Now that is interesting...Seems to suggest that he could possibly at least be making a guest appearance in TW.