I recently stumbled across a document that suggests Honda makes a kit to
add rear speaker pins/wires to the car's harness for pre-2004 cars which don't
have them. These headrest speaker installation instructions show something
called the "Headrest Speaker Sub Attachment Kit" - alas no part number but a good
parts guy might be able to track it down.
http://www.handa-accessories.com/S20...2kheadrest.pdf (see page 16)