Thus you can add, subtract or create any shape with-in the system panel. This obviously only affects this panel instance but it could be a fix for that one or two non-rectangular panels with in a bigger system.
This image is a simple shop front curtain wall, with the wall profiled. I have edited this instance panel to have circular holes in it.
Note: A limitation to this method is you will not be able to call it up in a legend view.