Hum, you are making me get ideas.  I have this large magnifying lens, and the sun here is really bright and HOT right now.  Might give it a try and see if it will scorch plastic really well, or just make a melted mess.  This lens is large enough that I once caught a 2x4 on fire with it.

Either way, I will experiment around a bit.  I have some old testors tube glue and liquid in storage.