My car is old enough that it came with an iPod 30-pin connector to feed the audio system. I currently have a ridiculous series of adapters to allow me to listen to iPhone 6s and simultaneously charge the iPhone.

The iPhone is in a Car mount , with Lightning port provided by an official Apple Lightning to 30-pin Adapter (0.2 m).

Since the Apple adapter has a very short cable, next there is a 30-pin extension cable (male to female).

That is long enough to reach the 30-pin socket in the glovebox, but the car only provides FireWire iPod charging voltages. So yet another adapter injects 5 volts into the 30-pin system feeding the iPhone via a mini-USB side port.

All this actually works (although I am embarrassed to have implemented such a thing), with the limitation that the iPhone only charges at the rather slow rate of 2.5 watts (actually less than that, probably due to all the cable resistances). This is the same rate it would charge from a straight up original USB 1.0 or 2.0 port, before all the fancy 'faster' USB charge rates became a common thing.

Is there a way to trick the apple Lightning to 30-pin cable adapter into allowing higher charge rates? What might be required?

I certainly can provide a high current source (say 2 amps) into the mini-USB side port on the DockStubs+ adapter, but it is unclear to me where the gating factors would reside that signal to the iPhone how much current is available.

I suspect the charge rate limitation is baked into the Apple 30-pin to Lightning cable adapter, but the Internet has been unable to reveal any information in this regard (at least, not from my searching).

Is there a spec for the 30-pin connector that allowed higher charge currents from the 5 volt source?
Update: This pinout shows USB data pins 27 and 29. Whether those have the same function in 30-pin world I cannot be sure.