Looks like the Asian PlayStation website has spilled some beans. On December 18, the Hong Kong PSN will be getting not only a Solid Snake Sackboy, but a character and level pack as well.
No prices are listed, but the items themselves most certainly are. There are individual sackboy costumes for Solid Snake, Meryl, Screaming Mantis and Raiden, a pack selling all four of those, and a "Level Pack", which looks like it includes stuff like creepy, over-sized manscenery.
There's of course no mention of this on any other PlayStation website - including the notoriously leaky Japanese one - so there's no guarantee these will appear globally once Thursday rolls around. But every other LBP update has gone live globally, so keep your Kojima-caressing fingers crossed.
UPDATE - This morning, the Hong Kong PlayStation site said the items were due on December 18. Since then, the release dates have been removed from the site (with no new date taking their place), so they may not be turning up this Thursday.