I decided to do this cause many ppl are asking.I first want to say that i haven't test it on Java but it works 100% on interlude off,probably on other clients too (i mean on every off,trust me on this).
3 steps and you've done it.
1)Buy any c grade dagger and add ability Rsk. Haste,i recommend Cursed Dagger
2)Go your life to 60% or lower and use any skill you want (frenzy,zealot,battle roar,etc,everything is working)
3)Then even if you remove the dagger,skill will reuse faster.For example,go your life to 30% or lower and use frenzy,equipped with the dagger,unequip the dagger use your sword and kill everybody you want,even if your life is 100% you'll see the reuse is much faster.Good isn't it?
I can ensure you that,this is working,tested on L2 Vendetta and that's working on every off interlude.
Enjoy ;)