The vents work on a pivot system, giving you 4 equal areas to work with. What I did on my '09 clubman was use 4 strips of electrical tape to shim up the areas. When done it made the vent tighter and held its position until I changed it. I did this about 4 years ago and they still don't move unless I move them. And the tape is NOT visible, I put it on the quadrants towards the rear, so that when it was returned to normal position it wasn't visible.

 

I’ve been thinking of doing something like this on my 2009 r55 since I got it a few months ago.
This will give me the push do do it.