The switch box cannot work miracles, so the way it works is to have a second LNB.
At this time, my setup looks like this:
What I will need to do is to work out some method of fitting a second LNB roughly as shown in magenta in the picture below. The criteria are demanding. It must be stable, it must be reasonable wind-resistant, it must be accurate, and it cannot be heavy.
Perhaps a more sound idea would be that which Ewen has taken, to have a second pole to the other LNB. This has been rejected due to lack of available materials and a mounting point. If you look the the pictures above, you'll see that the only solid anchor point below the perimeter of the dish is a horizontal section of the mounting, and it is not at a conventient angle. Ewen, by contrast (and from memory) has an up-and-down mounting pole to which a secondary LNB arm could be attached.
I envisage a number of light aluminium bolts and a cannibalised coat hanger. I have a rough idea of how this will all fit together in my head, I'm just not 100% certain if it will work in practice, especially regarding accuracy.
You can see what I came up with in part three.