Yes, I do this too, and it angers me because it proves that this datapath is possible to build. Double-dongle sucks, but it works. I marvel at how backwards apple can be when it wants to be. I wonder if this new headphone dongle they announced can be hacked to do charging.
It angers you? Apple has both options available - the adapter or a dock - and tons of 3rd party solutions are available, so you're angry?
My car doesn't have aux, so I've been achieving it with a Bluetooth FM transmitter. It's not ideal with occasional FM interference when traveling, but it's also ≤ $50 vs replacing the head unit, etc. And it works in every car.
Head unit is $20 these days http://www.ebay.com/itm/Bluetooth-Car-In-Dash-FM-Radio-Stere...
[1] https://www.amazon.com/SunbowStar-Universal-Charger-Adapter-...