Personally I agree with PZ. I don't think it needs to be in contract at all. I would just either A return money or B mention a while after birth that fees were weived due to stillbirth, or if family insisted you take money I would then tell them was donating it to SANDS or SIDS and kids in memory of their baby. As I do think it could put the fear into allready vulnerable familes.

A sympathy card is a lovely idea but would not advice mentioning it in that either.