It's possible to have Sorbs-like, yes, in Pomerania and along the Oder basin.
Now, are we talking of a people, or a people with a state there?
I think, if it's the second, you'll need something that would allow the federation of tribes (or federation of federations) more or less like Great Moravia did for Czechs.
Maybe having Obodrits managing to have their federation (called Duchy by Franks), allies with Carolingia enough to convert themselves will do it : you'll end with an acknowledged slavic realm in Baltic Sea.
It wouldn't be enough to resist the pressure of German, so I suppose you'll need Magyars failing to settle Pannonian plain in enough numbers to make German population more prone to settle Danube basin rather than Baltic.