Mike, your right, Robin gave me similar instructions for fitting Koni FSD's and I did make a half hearted attempt to access the top shocker mounts the way you suggested. At the time I was nervous about cracking the liners and did not really know what I was looking for. The attached photos show the rear wheel arch with the liner removed plus standard and FSD shocks and may help others understand the area they need to get at, knowing it can be done without completely removing the liner
Note the knackered bump stop (dark coloured one)
Cheers Spike