Two quick unrelated questions (Box2D and Surface)

[Jacob]

First, Box2D:

How would one create a sort of 'soft collision'? I want a body to be able to pass through another without difficulty, but have the other still affected. Meaning it is displaced on the collision, but not restricting it from passing through the first body. Think of it like a body contacting water, the water is displaced, but once the skin of the water is broken the body can pass through easily, with a slower velocity. I want like that, but without the velocity slowdown. Or with it. I'm really not picky.

Second, Surface Object:

I know this is possible, but I've never used the Surface object and don't quite understand it yet. Basically, how would one create a coloured polygon, with an actively changing set of global coordinates for the positions of its vertices?

[LB]

Make it go reeeeeeaaaalllllllly fast but don't set it to be a bullet?

You'd be having to clear the surface object and redraw it every frame.

[Jacob]

Neither of those help. The object can't be going really fast, that isn't the point. And I don't know how to make a polygon in the first place with the Surface object.