blah... I think totally oposite than this way of thinking.
I make up a melody in my head that fits the music and then just use the scales to find an easy way to get around the fretboard.
The idea of using scales to make up leads to me just ends up making all your leads sound like a bunch of scales.

Why don't you guys just hum a melody to the background music and then find the notes.. then you can use your knowledge of scales to find the best finger positions?