so....
take your friend and dragon. go to the place where your friend can kill mobes rather quickly. Summon the dragon. Your friends starts killing a mob, but doesnt kill it. You force your dragon to kill the same mob and do not touch the mob. After u see that your dragon made 1 successfull hit (there is a visual affect for that) your friend should kill the mob. You will recieve 0 exp, because all exp will go to your dragon. You MUST not shoot or engage the mob, but u can heal/buff/recharge your friend. And your friend must wait for 1 successfull blow from dragon and only after that kill the mob.
this doesnt work since the dragon gets the xp proportionally from the damage he has caused to the mob ... if he hits only 1 time, he will get 2xp, 2 times = 4xp and so on ...