Although I won't help you with that.
My I suggest something? In order for him to avoid selling something for an amount of BTC, which 5 minutes later could be worth less than 5 minutes earlier, sell items with a few % higher in bitcoins to ensure he gets his money.
I was thinking to offer a little discount. Right now, he's using paypal, so there's room for that. He'll most likely just cash out his BTC instantly to pay for his suppliers.