Well.... I've seen it stated on a different forum (by a guy who claims to age his big beers for multiple years) that you don't need to pitch any more yeast. It might take a while for the beer to carbonate.... but you've already waited 50 weeks... what harm is there in waiting another 6 to 8?
That said, I'd probably pitch more yeast. I would mix up my priming sugar and pitch a packet of dry yeast into it. When it started to foam a bit, put it in the bucket, rack your well-aged beer into it and bottle.
Please follow up here to let us know what you decide to do, and what the outcome is like.