Have you tried printing the other edge first?
No...too lazy. Came running straight to the forum!
But I thought of that, too, and I'm going to try it. Guess the HP interface, for all it's clunkiness, beats the Canon in this regard.
UPDATE: Starting the prints from the other side does the trick. It allows one to unload the media, then reload and start from the beginning of the roll even once it's been printed on, as long as you start printing from the left side. Bingo!