I seem to recall there being a one command operation that allowed flanges to be created encased in a flat sheet metal surface.
Apparently this was a different software from years past. Because based on the thread link below, there is not one currently.
There should be though. Seems like it would be a rather easy command to use that would save so many steps and command sequences.
See attached thread.
http://forums.autodesk.com/t5/inventor-general-discussion/sheet-metal-bend-within-a-face/m-p/6508974...