I did a search and didn't see where this was mentioned before, so I thought I would.
I saw this product for the first time this week, Bondic
http://notaglue.com/It is like the material they use on your teeth, it is a liquid until you shine an ultraviolet light on it and then it solidifies.
It can be sanded and painted. It is sold as a "liquid plastic welder" and would be pretty handy to have in your toolbox.
I can see some uses for it in our hobby, but it is a little pricey.
Mack