Unfortunately this feature has not been developped yet as part of the managment portlet. It is only possible to do it with an XML file that will create it.
btw, i have a bug in the management portlet :
when you create a new instance of portlet without specify a name for this instance, it's never more possible to destroy it when the instance with no name is added in a page.
moreover, i ask myself where does the portal store this information ?
i just can find a trace of my instance of portlet added in page dynamically ?
in the DB ? in xml files ?