Success!
Thule fixing kit 5178 does the job. Paired with Thule footpack 7105 and Evo 135 bars. I think you can use other Thule footpacks and there are certainly other Thule roofbars. Trick is to follow the spacings as per the instructions precisely, fully loosen off the foxings when attached to the footpacks (use supplied allen key to loosen off as much as you can after slotting the fixing into the footpack) before placing, per spacing specs, onto roof. When on roof, make sure footpaks are properly seated into roof channel and then start to tighten one side, only do about 3 turns before doing the same on other side. Alternate between sides using the 3 turn method until each sides are torqued. This method prevents the footpack on one side popping out of the roof channel before the other side has been fully torqued. It helps to have tow people.