Dan,

You can't.

Another approach, instead of using a Parameter Query, is to put an
unbound textbox on a form where you are running the report from, where
the user can enter the Area criteria.  You can set the Default Value
property for this textbox to "South East".  Then, in the query criteria,
in the place of the existing parameter prompt, you refer to the textbox
on the form, using syntax such as...
 [Forms]![NameOfForm]![NameOfTextbox]