I have several halter dresses with built-in shelf bras. These are fine and adequate support since I'm a small B cup. However, I wouldn't mind a bit more "oomph," if I could find a product that I could insert into the shelf bra ... and NOT cups that need to be "sew in." I tried that. Too much fuss. My question is ... do bra inserts (like Sassymax, etc.) work in shelf bras? I keep thinking inserts will shift and fall out unless I sew them in (which I don't care to do). Anyone with experience in this department?