I must first apologise because I can't find the thread and don't recall who posted the tip. Anyhow, thanks are due. I messed up a couple of bits of wood [didn't tighten the fence hard enough when routing and thought I'd been pushing too hard], and all I had left was a badly planed end of the original board. I'd taken it since they only charged for a good section, and the bad end still had some good material. But I needed most of the length.
So.... I took the hint and hot-glued to a piece of 1" MDF, and ran it through the 12" planer. A few mild passes to not give too much stress to the setup, and it worked like a charm. Removing the board, one side planed, was dead simple, and it didn't damage the MDF, which can be used over and over for that purpose. Turned it over, lowered the planer blades, and did the second side easily. The board was slightly bowed, and one side had a deeper cut in the original planing, and in fact was a bit wavy. So I supported the center with a shim and a spot or two of glue there also, making it quite solidly attached to the MDF, no likely give in the center.
Thanks!! Two brand new pieces that now fit perfectly from a board of what might have been firewood.