Dave would usually play the Fab Four's X-mas greeting before the song, not after, so I think he's taking a pass this year.
Speaking of Xmas greetings, anyone heard any clues as to whether he's doing a final Foghead Xmas Card set next Friday? I'd love to hear it, but he'd have to put it together at the station, as I'd bet his home studio is boxed up and ready to go on the truck by now. And those things are no small amount of labor.
Nothing has been said -- my guess is he doesn't want his last "live" 10@10 to be the Xmas card, but he could solicit greetings early next week and record one for playback on the 24th. (he'd just have to voice-track; most of the work would be Greg's or some techie)
ETA: Peter actually asked that very question the day Dave made the big announcement; Dave tersely replied "it's 2 months AWAY, Peter -- I'm not thinking that far ahead!"