Using the PDF Creator you can use the Width and Length properties of the Page object to define whatever page size you need.
This can be done directly from the user interface if you have the end-user version of the PDF Creator or programmatically if you have the developer version.
e.g. pdf.ObjectAttribute( "Pages[1]", "Width" ) = 12000 (the values are in Twips, i.e. inches * 1440)