'Buffer dots' arrived today and are now fitted. I've lightly scotched the fitting points with fine sandpaper, cleaned the area, (well whole cages TBH), with brake cleaner to remove any residue and also any remaining GT85, then applied them.
I've only tried a bottle in them with the bike stationary, but you can definitely feel more friction now when you come to remove it, so hopefully my new bottles will arrive tomorrow and then I can properly test the whole arrangement this weekend.
As long as the dots stay stuck I think this will will work fine, if they don't then a drop of cyanoacrylate may be in order