AutoCAD Inventor :: Extrude Cut From 3D Sketch

I know my subject is somewhat mis-named, because I gather that you cannot really extrude from a 3D sketch, however I am looking for a way to accomplish what extruding a cut from a 3D sketch would accomplish.

The problem is this: I have a simple 2D sketch that I've projected onto a curved surface (imagine a square projected onto the outside of a hollow cylinder). Now that I have a 3D sketch on the surface of the cylinder, I want to use that sketch as a "cookie cutter" through one wall of the cylinder.

If I were to simply extrude the cut from the 2D sketch, the "cookie" is wider at the edges than at the center. I want the cut to be perpendicular to the projected 3D sketch at all points. 

I've attached a simple example that illustrates my problem.