Speaking to ITV's Daybreak about the 50th he said:
"“I’ve heard lots of rumours, none of which I’m allowed to tell you anything about. I’m privy to them actually.”
He then added:
“I have got a copy of the script which has got my name embossed across it. So it’s top secret, but there’s other stuff, lots of other things that are going on that people should keep their eye open for around the 50th anniversary special!”
Whether the script was just a gift for a past Doctor or was indeed an indication that he will be seen in the episode remains to be seen and we'll have to wait until the 23rd November to find out.
Source: Doctor Who TV