Extrusion along normal vectors?

Hi everyone!

I created a few arcs with different radii in different heights, transformed them into polylines and extruded these with a Unit Z Vector. What I want to do now is to extrude these generated surfaces towards the central point of the arc, but only with a certain extrusion distance. I tried to show what I mean in the third picture.

I'm trying to extrude along the normal vector of every single face, not along one vector for the whole surface. Is this possible or can you propose a good workaround?