Damn...I wish I could get the video to load. *kicks YouTube*

He is definitely doing it as a wink-wink-nudge-nudge. He knows the controversy that song stirred up, and he's just continuing that implication. The song's sort of become an entity of it's own.

I'll just take a dive into Justin's psyche here for a second and venture a guess that he thinks that she needs serious help just like everyone else in her life does. Doesn't matter if he's not technically "in her life" anymore. He was for a long time and I'm sure he knows what's going down: Britney's really troubled and she's in denial about it.