Move mouse over center of opening then tap Tab key until the outline is highlighted, then click.
Note, tapping the Tab key allows you to parade through all possible selection options based on cursor position and this technique can be used with other modeling tools.
Use Numeric Input palette and/or Tool Options palette to enter parameters such as Width, Height and Justification (Left, Right, Center).
You can change the parameters anytime by selecting the frame object with the Pick tool and clicking on the Parameters tab in the Tool Options palette.
