I have not done it, but I would use a temperature controlled hot air gun and some suitable forms to bend around. If you want a right angle bend, construct a right-angle form with a rounded corner to use as a pattern. Then lay the sheet on a flat surface and carefully heat along the crease until it is bendy. Possibly cover the flat parts each side of the bend with foil to keep them cool. When the sheet is soft, carefully bend it along the crease against the form and hold it against the form until the plastic hardens again. Use your ingenuity and experiment a bit.