@ JuhaW, would be nice if you can explain a bit more, i quite do not understand how to use your short tipp. Is it an addition to eppo´s solution to keep the faces flat?
Honestly i was confused too a bit. But snapping could be another option. Never used it in such a way, nice tip!
I did not had the luxury for SZ0 coz i used Grid and squares had corner edges connected; my fault for not looking into image enough.
Both methods are nice ways to do the job. I think using the Shrinkwrap mod is a bit more flexible, you can change the shape-object on the fly and you can adjust the shape´s position in 3D Space and the extruded faces will follow.