I believe his question was "is there a way to change the default size for the clipboard" not "is there a way to make the clipboard bigger" =)
in reply to the real question:
If you right-click on the +/- sign it will zoom the map in, and this level of zoom will saved (until you relog i think)
If you left click on the +/- sign, it changes the size of the clipboard itself. If you are shrinking the clipboard, it will retain the clipboard size. If you are enlarging it, it will not retain the size if the clipboard boundaries go off the screen.
have fun,
Kraquen