Damn, that is old school genius!!Found this online.. I don't know how it would work with fishing boots
Extra W-i-d-e Feet
Freeze them. The boots that is. Take two puncture-free produce bags commonly found in a grocery store. Place one bag inside the other. Stuff these doubled-up bags down into your boot, as if you were trying to line the boot with the bags. Lace the boots up with a lacing tension similar to what you would use if your feet were in them. Now carefully add water to the produce bag. Avoid getting water in the boot lining. When the bag contains enough water to fill the entire boot area below the ankle, securely tie off the top of the bag using several wire twist-ties. Now pop the whole set-up -- boot, bags, and water -- into the freezer, where the liquid will solidify overnight and expand. This expansion is your widening tool; you can imagine what this does to the forefoot of your boot. Viola! Your D width is now an E. If you need to drastically widen the boots, use this procedure in multiple stages, using new bags for each width stage.
I am fan fan of the "shrimper boots" by servus. I believe they do come in a wide width.