Kathy,
If the little guy can use a straw at all, a straw trainer might come in handy.
 Mom gets a soft palstic squeeze bottle with a spout (the type they sell in
chocolate making/cake decorating stores) and some aquarium tubing.  cut the
tubing a few inches longer than the bottle, cut the spout leaving an opening
just large enough for the aquarium tubing to fit snugly through, and thread it
to the bottom of the bottle.  the supplement is put into the bottle, and the
bottle is gently squeezed while baby sips from the tubing "straw".  Mom or dad
gradually decrease the amount of squeezing as baby learns to suck from the
straw.  stole this one from the OT literature (occupational therapy).  another
tip:  if the supplement is very cold he might be more willing to drink it, as
cold will be a novel stimulus, and also dulls the taste.  no artificial
feeding product, no matter how necessary, tastes as good as breastmilk.
Let us know how this little guy does.
Catherine Watson Genna, IBCLC