ya if you know what your talking about then your golden, make sure you literally get all the information in your head and ask them to ask you any question about it.
Next make sure that they have ABSOLUTLEY no responsilibity for the cham. If they truely feel like they won't have to worry about it you're chances will sky rocket.
Next show them how bad you want it, try and come up with a reward system if they don't agree right away, like you get a good grade in school or get a job or something like that.
last don't just shutdown everything your parents say, take it into full consideration
oh ya! and make sure they know how serious this is to you, just act as mature as you can about it and show them that you are more than ready to take on all this responsibility, and hopefully you are well aware of how much responsibility that really is.