ArcGIS 10 SP1. In the dialog Data Frame Properties, in the tab Data Frame, in the area Extent, the menu provides the option Other Data Frame. The option Margin only controls the scale (which is not at all clear from the dialog; I had to play with it to figure out what it does). In addition to clearer labeling (e.g. another area that says Set Scale), what I want is the ability to offset the second frame from the first, e.g. by 7 inches in the paper coordinates.