I have seen this as well. When a baby develops a preference for the
finger...you have no choice but to switch methods. I doubt that a rubber
nipple will help, unless mom wants to go to full pump and bottle. How
about cup feeds? "Starve the suck, not the baby" kind of thing? If the
baby gets nothing else to suck on...perhaps the breast will start to
look good to him. This assumes, of course, that he is not struggling
with weight instability etc
Good luck
Susan Keith-Hergert RN, MS, CPN, IBCLC.