What I use for lips, is not exactly Lexan, but should be pretty similar stuff, called Axpet, from Bayer. I make just straight, slightly curved lips, not complicated shapes.
I use a template for bending. You need two cylindrical objects as template, that fit into each other, with enough clearance between them to accomodate the plastic strip/sheet. I use two glass beakers, used in laboratory.
I cut a strip from the plastic sheet with a length of the circumference of the smaller beaker, and width of the length of lips to be made. Bend the strip into a circle, put into the bigger beaker, and fasten with the smaller one to fit closely around the glass wall. I hope you can imagine it, in spite of my poor explanation :-D
After that I put it into a lab heating oven for a minute or so, then remove and let it cool. I think that household cooking oven will do the same.The suitable temperature for my material was 100-120 C, but it may differ with Lexan. I hope that you or others can adopt this method for Lexan as well.
folk