Well,
I bought a wireless fast charger from here:
https://www.ebay.com.au/usr/megoshop2012?_trksid=p2047675.l25592IN1 QC 3.0 Fast QI Wireless Charger Car Holder Mount For iPhoneX For iPhone8 MG
$23.
After considering how I could use the mount etc, I dismissed that idea and pulled the guts out of it. I had already made up a simple phone holder out of a piece of sheet metal folded top and bottom, so I glued the flat coil onto the front side of the holder so that it was positioned near the middle of the phone, then drilled a hole through the metal so that I could feed the wires to the electronics module which I then mounted on the back side. I then wrapped it all in cloth tape (100 mph tape) for waterproofing :).
Surprisingly enough it worked perfectly and was able to provide enough power to charge my Galaxy Note5 phone whilst using it for navigation, music/podcasts during my ride up to the national rally.
I say surprisingly because I had installed one of those dual USB adaptors in place of a cigarette lighter socket eg:
https://www.narva.com.au/products/81134BL which doesn't support Quick Charge, but the system still supplied enough power. A proper QC compatible adaptor would be much better and would charge the phone in a 1/4 of the time of my current setup.
I think this setup could also be used with other phone holders provided they can withstand the phone being pushed out by an extra couple of millimeters.