Although the Centre mounted SatNav is a neat solution, I find it takes more than just a glance to see it and involves moving your head and refocusing. I would have gone this way myself, but tried the idea of securing one to my tank bag. I didn't like it.
Instead, on all 4 of my ST1100 / ST1300 I have drilled into my plastic shelf to mount a ram ball so that the satnav sits behind the screen.
The pics below show this on my ST1300A6 - which I took a few years ago. A ramball mount with a flat, diamond shaped base and two bolt holes. I have cut two pieces of very thick rubber sheet and a piece of thick aluminium to be exactly the same size as the diamond shaped base. The ramball mount sits on top of one rubber sheet. Underneath the fairing shelf is another rubber sheet and the thick alumium sheet. The 5 layers are bolted together.
I was worried that over time, the shelf plastic might crack - but my A6 did 70,000 miles with this mount before I sold it, and I have exactly the same arrangement on my A9. Neither shelf has shown any signs of stress (apart from having 2 holes drilled in them).
Getting the position dead right to allow the screen to be raised and lowered; making sure that the plate and bolts underneath didn't interfere with the screen mechanism; making sure that it could be seen easily; and choosing an arm which didn't amplify the vibration of the bike in motion - were all considerations.
I find that this is easy to see at a quick glance. It is out of the instrument panel. It isn't in my direct line of sight. My pillion can read it over my shoulder.
The wiring passes through one of the small rectangular shaped strengthening notches in the edge of the shelf moulding. I have cut out one of the rectangles.
If anyone wants the precise details of where and how - I'd need to get into the garage and take more photos and measurements - but let me know.
Of course, if money is no object, then you would need to be looking at the Migsel mount. Designed to fit into the push clip holes. A very neat solution. Google Pictures Migsel Mount ST1300. But it sits directly in front of you, which I didn't particularly like.