To make a template out of thin panel wood, with the exact size hole you want, then just carefully cut around with an exacto knife. Hold the template in place with 100 MPH tape (get it at a military surplus store)
As far as what's behind the leather, sounds like you will need a jigsaw, with the right type of blade. Keep the template in place, until the cuttin's done, or...
__________________
James Madison, father of the Constitution, said, "If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy." He also said, "No nation could preserve its freedom in the midst of continual warfare..."
~~~~~~~~~~~~~~~~~~~~~~~~
http://www.standdown.net/index.htm