Some of the E89 models had a 12v power socket fitted in the dash under tray below the glove box, mine didn't but, the moulded port for it was there.
So, I bought a cig. lighter body from eBay which was a perfect fit, along with the shortest double USB power adapter I could find (total length 35mm.).
Using an "add-a-fuse" and about 60cm of dual cable I've wired it from the fuse box.
An added bonus was a pack of 2 of these USB connectors,
which when connected to the dashcam power cable (which now seem to come with USB plugs) I secured with a couple of laps of insulation tape.
With the cable fed through one of the heater vents holes it plugs in with very little protrusion.
Another USB 2 port socket is for another day.
Tomorrow I'll finish the new DRLs in the front bumper.
Gloss painted grill trims refitted today.
Tony.