Thanks for the ideas! Here's how I did it.
Got a RAM ball that mounts with a M8 bolt, #RAM-B-367U
Wanted to use 3mm thick L-shaped aluminum, I knew I had some, but couldn't find it. Took a piece of 80mm x 40mm and cut it to L-shape.
Made a slight bend to match the lines of top console.
Test fitting, marking four holes and drilling. Used couple of bolts with three nuts as spacers between brackets to secure it in place. Drilled small guiding hole through plastic and aluminum bracket. Then 8mm hole to bracket and 11,5mm to plastic. Trimmed bracket to its final size, some filing and sanding to round corners. Put some self vulcanizing tape around the base of RAM ball to hide clear aluminum and give it a snug fit through plastic cover. Also found the piece of L-shaped aluminum I was looking for earlier..
And there it is.
I'll do the wiring later. GPS's battery is good enough for short trips.
Got the wiring done. Just soldered the leads together with the heated grips plugins connected to ACC2. Enlarged the hole for RAM mount to get the power plugin through and put a rubber grommet to give it a snug fit.