Hey Skinjob!
You can use a simple 24ga wire wrap lead as a jumper. The pigtail for the 3.5mm jack depends upon the type of cable you choose, but it’s simplest to make a cut alongside the existing cable’s strain relief, and you can wire tye the cables together for support.
If you have a cable with strain relief, then you can make an individual “port” for the cable in the connector housing.
Bob :smileyvery-happy: