Hi Martin
You are right in what you say - you can flip the mirror arms further out. I used to do that when I towed with a 110. Basically the mirrors have two settings, one is with the arms at approx 45 degrees to the door , the other is with the arms at 90 degrees ( although when set like that the nearside one can be a bit awkward to see).
The other thing you can do is slacken the ball joint at the bottom of the mirror head, cant the head over and then re-tighten.
If these options do not work for you then Land Rover do sell longer mirror arms ( intended for the Military vehicles which have the spare wheel mouted on the side).They also sell spacer blocks to go between the mirror arm and the door mounting.
Hope this helps, if you need any help with part numbers please let me know.
Nigel