I wandered this, I think you just buy the other jets with the 6mm pipe and insert them yourself!
they also sell the 4 way push fit to connect 4 jets to your pole hose. They have all the bits on the site.
I was going to email Alex and ask if he would drill me some hole for another pair so I could try 6 jets, as when I have tried drilling myself the holes never end up straight. Never did though.