Kathleen:
My experience has been that it works best to have the AAP on your side when trying to change pediatricians' actions.  I'm currently chipping away at my office's acceptance of ABM company money for printing our patient literature and chart forms...
At the AAP internet site (www.aap.org) I obtained an official AAP statement titled "Hospital Practices Influence Breastfeeding" which, while short, does speak of the negative impact of ABM samples in hospital.  My brain says that this has also been addressed in an article in Pediatrics (the "green" journal) in recent years, but it may be mistaken.  Too early in the morning.
I would *really* like to know more about how the formula reps make grand rounds in your hospital.  At first I thought I read that wrong.  Do you mean that they are actually interacting with mothers and babies??!!  Please send details.
Good Luck with your efforts.
Willow