He mentioned that he is trying to adapt his fuel pump to use Lightning and it requires a refund address because their is a pre-payment required. Rusty Russell responded that he never thought of the requirement before but suggested a flag in BOLT 11 which says it wants a refund address, and putting the refund information in the payment onion itself. The refund requires basically another complete BOLT 11 payment request, which would be only known to the final recipient. There's currently a brainstorming item to allow for more information to be crammed in there. Rusty filed a feature request for this idea.