If you actually send the money one could (juridical or morally) consider that you agreed upon this scheme and you will see you stucked in a difficult situation. What do you do if you sent the money and he considers this as an agreement and keeps sending you money in envelopes? You would be forced to keep sent him bitcoins.
I'm a fan of totally anonymous transacations but beware of becoming a money launderer just by beeing nice to someone how doesn't disclose anything but a bitcoin adress (on purpose!).