[NiLuJe]

@melovesflying: See the comments about using LS in the first post.

But AFAIR:
Hmm, keeping the books in the collection on the Kindle side is easy enough (rely on using incremental updates, and do an export in LS before pluging in).
But keeping a full sync with a Calibre column, trickier, since that's incompatible with incremental updates, and I don't even remember how the Kindle -> Custom Column stuff works (being something that I've never used myself).

Might be possible, but doing the same trick without incremental updates will make the the two types (Calibre/LS) of imports/exports slower if you have a large amount of books/collections.

I think some of that stuff is detailed in the first post.

EDIT: It is, briefly. And apparently Yes/No columns are supported for import, so, hey.
Make a backup of your Calibre database just in case, and go for it?