inverse of pocket

I am using D2NC <http://www.d2nc.com/index.html> and want to make a round "boss" on a rectangular surface. So this is the inverse of a "pocket" in that I want to leave the stuff inside the circle and take away everything else. How do I do that? I can "contour" around the the hole, but not further than one pass.

I think what I need to do is "pocket" outside the hole, but inside the outermost perimeter.

Thanks, Chuck