Most results that Google will throw your way when looking for the best way to attach your GoPro to a ski pole for those great sweeping action-panarama shots will show the use of the official Handlebar / Seatpost / Pole Mount but with the addition of loads of rubberised tape to thicken the point of contact to meet the mount’s minimum diameter.
This is no longer the case, the latest incarnation of the same official mount is identical bar a few vital additional bits and bobs, most important of which (for this application) being the rubber sizing adapters.
It is not obvious that these new bits are now included but this now makes for the perfect mount with no messing about with tape etc.
I got mine from the official site.
(On a side note, I did notice the new official Sportsman mount which is intended for gun barrels, hunting bows etc… I thought this might be a great option for a ski pole because of its quick-release mechanism, but it is far too heavy so i wouldn’t bother, just grab the above (for much cheaper) and you’re good to go).