A section through the cut is an ellipse. Here's something that might work. First, figure out the height of the angle. on a 2" tube, a 45° cut would be 2" high. (low point to high point) Draw an ellipse with the height as the X value, and make the Y value 180. (180°). Erase half of the ellipse (left or right half), copy flip and paste as shown. It should now be 360 tall, for 360°. The X should be the distance traveled. Save as R12 .dxf, and the ellipses will be converted to polylines automatically. Create gcode, and swap the Y with the 4th axis A? C? Because it's so tall, the resolution may not be good enough. The picture is not to scale, it will probably be much taller.
You may also be able to do this with an Excel spreadsheet.