I have only seen this trick done twice and the two jugglers used different methods, I will describe them both here.
The first method, used by an American busker in Montpellier, was just an extension of the double kickup with the third club placed on top of the other two:
The second, which I saw at a juggling convention, was just a three club start arrangement placed on the foot and kicked up. Of the two this is the one that I would be more inclined to practice, because it creates a larger height difference between the clubs, giving you more chance to get the pattern going.
Kick ups don't stop here either, someone in Russia does four.