Shouldn't be too hard, really, just have to have a length-one route to ourselves with a dummy SCID (zero?) generated by the router. Then if we see it we immediately generate a PaymentSent and PaymentReceived event and put it in the outbound payment set as fulfilled. We'll have to think a bit about how to ensure persistence is guaranteed but maybe we just handwave that away for now and rely on the user checking the pending payment set and seeing it missing?