Here is my tiny Lightning Dock. You have to buy one of those iPhone 5C Docking Stations with Lightning Input and Lightning/3,5 Jack Output. Those fake ones of ebay won't work.
At the moment (here in Germany) you can get them online for around 2$. Amazon sells them as a "Plus Product" for around 5$.
Be careful, as the original dock only has a Line Out port, the volume cannot be controlled by the headphones or iOS.
Fast Print (worked for me)
Extract the circuit board from the docking station. Be careful with the tiny Lightning Connector Cable (it will easily get detached from the circuit board and it is a small pain to reattach it).
You'll have to shape the connector cable like a little "S" (photo of circuit board) so that it fits correctly. Try to attach the both flat grounding cables to the connector.
Insert the connector first, then lower the board and lock it (the both sockets) into the two holes.
After that, fill everything (or just the connector) with hot glue or whatever you like and put the lid on top.
Et voila! A very tiny (as tiny as it gets) connector for listening to music and charging your iPhone 7.