I switched the convex mirror to the left mirror and driled inside the cup which has the indentations into which go the base of the mirrors. Currently you have a setting for LHD. It was a very hit and miss operation and I originally estimated incorrectly where I would have to drill, but I am not patient and unskilled.
It is not ideal, but they are in the right position and stay there most of the time except when you close the door sharply. But high speed on he motorway, not a murmur.
Someone out there must know a more scientific and reliable method.