In biochemistry an excess of a thiol, such as 2-mercaptoethanol or dithiothreitol (DTT), is often used to reduce the disulfide bonds of proteins. You would then need to remove the side product and unreacted thiol. I have no reason to think that sodium borohydride would not work unless there are other functional groups present. Occasionally phosphines such as TCEP (tris-carboxyethylphosphine?) are used to reduce disulfides when the pH would be too low for DTT to be effective.