Jay, While you could sow almost any green manure in February, it isn't likely that anything will germinate until March at the earliest. Until then, without some textile or natural mulch, you'll be feeding birds. Hairy Vetch, Chickling Vetch, Field Peas and most of the Clovers are good early germinators, but not that early.

How about a good thick layer of mulch for the winter? Spread shredded leaves, straw, etc.. It would at least do the surface soil some good and wouldn't look as much like a bare patch of earth.

Given the weather we have been having so far this winter you could plant something like Cereal Rye now and still have it germinate and grow some.

I successfully sowed Cereal Rye a few weeks ago and I am much further north than you. There is a winter growing type of oats as well but the species name evades me right now.

It all depends on where you are. I could plant a million seeds right now and I'd just be feeding the birds.
I'm not even going to think about working the soil until mid-april.