Gizmo...
I'm with Oly, as I can't see where to move a single post. Looking at the code in movepost too it is obvious it grabs all the replies to the post you are moving, and ships them along.
Unless i'm missing something here, I don't think this is an option.
I made the mod as oly is asking for above, but if the functionality already exists I'd love to see where to find it!
chillin