After updating from 3.5mm, to iPod Dock Connector, to Lightning, I finally found an RCA to USB that also provides power (spliced into the phone connector under the dash). Now I can plug whatever I want into the USB and get audio and power. I think it is the best solution short of a new head unit.
My setup goes from the HU connector to RCA, to ground loop isolator to eliminate any hiss/whine, to this:
PAC USB IS3301.
Don't be restricted to 3.5mm, an adapter to RCA is a common audio adapter you should be able to find at Best Buy, or RadioShack if you can find one. I think Home Depot might even have them.