Right - had a look around the car spares place in the Audio and Interior bits and bobs sections. Found an audio mount which is almost exactly the right size. Its from an adapter plate for a FIAT to allow a standard DIN head unit to replace the built-in non-standard sized one which fails quite easily. It is even the right colour to match the interior.
I didn't get it. They wanted £16
EDIT - Going to look at a pillar mount like you mentioned and may even strip the SG2 to look inside, unless someone has pics of a disasembled one...