Well I went ahead and pulled apart the bootlid trim using mostly brute force and didn't manage to break anything. For anybody else wanting to fit a reversing camera to a CLC here are a few tips:
1) The video lead should go through the right-side cable boot. The left contains all the wires for the light clusters, so there is not enough room to get the video feed through it (took many hours to figure out that one!). The right boot just contains the FM aerial feed and heated rear screen, so there is plenty of room to squeeze the video cable through.
2) Start by dismounting the rearmost felt liner in the boot lid - just pull out the centre pins, then prise out the outer pins, and drop the felt.
3) Now prise out the rhs side trim panel. Just use brute force to prise it towards the centre of the rear window.
4) You can now drop the rhs of the centre trim panel. Undo one screw, and prise out with a big screwdriver the orange mushroom connector that I photographed above. Not totally necessary to remove the LHS of the centre panel - but if you want to do it you will need to mirror repeat 3).
5) You should now have access to the boot hinge rubber boot and can pull it off gently to get the video cable through it. Obviously you will need to use some sort of nylon puller cable, and a bit of detergent helps - but not too difficult.
6) You can now feed the video cable through the headliner and A-pillar. No need to drop the whole headliner - just pull it down from the rubber door and window seals. You can use a lot of brute force without breaking anything. Use a trim tool (or credit card, or plastic bicycle tyre lever) to squidge everything back together.
Actually now I am doubting myself.
