This system is by Ewoud Bras who has started making and selling complete shafts in Belgium under the name Bike Polo Gear Europe... http://bikepologear.eu
When I got back from Europe last month... I saw Dustin doing the same thing with a little different hardware here: http://www.guardiansbikepolo.com/?p=255
All the details are in the pictures.
Step 1: Euro Method
Even thought the 6mm bolt is only slightly smaller than the US 1/4" bolt/insert , the brass insert fits better in the shaft than the equivalent 1/4" drop in inserts available in the US.... you might be able to cut the shaft higher but I decided not to at this time...
I found an old link to an EBAY site that was selling these brass inserts as Molly Brass Wall Plugs..
Molly Part # m53610. M6 x 24mm x10.
Step 2: US Equivalent
The inserts slide down into the tapered ski pole.. but because they are larger than the euro insert.. it requires a slightly longer bolt... this adds a little weight.. albeit not much... but slows down reaction time...
The US insert slides into a 3/8" hole.. on both styles there is a small lip on the insert that I grinded off... you'll understand when you get one...