Some doctors are doing fat injections -- where they take fat from your stomach and inject into your breast -- but it depends on how big the hollow is -- it cannnot be used to fill a large area.
I had a unilateral mastecgtomy with DIEP reconstruction and had fat injections to fill a small hollow at the top of the flap area.
Where are you located? You need to be in a major city at a major cancer cetner to get the latest treatment.