If you enlarge the seat by placing a piece of plywood on it, then you can make it about 2" wider on each side, but don't make it any wider, since then you will have to make your "Wings" 2" wider and I don't think they would be as safe. To me the seat on the cheap standsis fine,it is the foot room that isthe problem. Some folks have suggested to use a single piece of plywood, hey if your stands are not up yet or your taking them down, then by all means make the wings out of 1 piece of plywood screwed together tow thicknesses and drill a hole for the support to go thru, thatwould make it stronger and safer. Safety is the key. Stronger and safer. I use 3/4 pressure treated plywood, since I fell deck boards and the like sticking out 7" just wouldn't be as strong as two 3/4" plywood stuck together.
Chap