Robin,

One more idea would be to have a towel or diaper nearby.  When Mom has her
first [and probably her most forceful] letdown, she detaches her baby
momentarily and lets the milk flow into the diaper until it slows.  Not much
will be lost, and hopefully the subsequent letdowns will be more managable
for her infant.  Also, another nursing position she might experiment with, in
addition to lying on her back,  would be a football position with his head
quite elevated.  This could help keep the baby from feeling like the milk was
squirting down his throat.  You don't mention the age of the baby, but I
suspect that as he grows, the force of the letdown will be less problematic
for him.

Laurie Fjeldstad, RN, IBCLC
Madison, Wisconsin