In Naruto Shippuden Ultimate Ninja Storm 2 how to do I substitution Jutsu at will?

I gotten all they way to where I have to fight pain after naruto turns back to his normal self. An up until this point i have just been getting lucky with substitution but in this fight pain is really hard and ninjutsu arent really working because he blocks or substitutes. And its hard because when i try to do a combo on him he will substitute him self and go to town and i keep tryin to do substitute jutsu but it doesnt always happen....is there a certain time i have to press it or do i need a certain amount of chakra or what...im sure i will win eventually but i just wanna know how to do substitution when ever da way da computer does it