I used to pump one while the baby nursed the other. Milk production increased by doing this as well. I would usually get about 6 ounces every morning with doing this.

It could also be that if the baby has started solids, milk production has decreased because hunger levels go down once they are eating cereal, etc.

If all else fails... My babies had both breast milk and formula (Carnation Good Start was easy on their tummies). Both of my kids are now BIG at ages 10 and 12 and doing great! They survived a little bit of formula.

Hopefully the baby is still in practice with the bottle as that may be a more difficult one for the sitter -- I speak from experience having babysat a breastfed baby who didn't like the bottle. What worked in that situation was going to a sippy cup. Avent makes some nice ones with rubber type sipper parts that are good for 6 months and up.