To the best of my knowledge there is no such functionality. I get a "circular" detail by:
* Making a rough spline around the area of interest
* Once the view is defined, a circle is shown on the "source" view.
* In the view properties of the detail view I redefine the spline, this time picking points around the circumference of the circle that is already on the "source" view.
* This whole process is a bit more tedious if I'm making a detail view with an elliptical callout.
I've never had to do a rectangular callout, so don't have any advice on that aspect of your query.
