i did but with dupe bug, and even then its not worth imo, just stop at 20
you need a companion, give him item that can be used as exp for armor/weapon, go to anvil and pick something to upgrade (like broken sword), click item that you gave to companion as many times as you want (it'll not be used), do not upgrade and just back out from menu, done. it's probably fixed in 4.5 but in 4.4 still works.
p.s. ability crystal giving most exp.