the tin foil is for the underside of the lexan to make sure it doesn't melt, so you can use tape, but the adhesive might melt, and then melt the lexan.
If you do it right, you can fold and crumple it so that it stays without the tape. Just make sure there is no exposed lexan.
Also, if you don't want to do it in the oven, the method that danielkh posted will work. Maybe. I haven't tried that method yet personally.