how to say no.. without using no...

You could say...
I'll take a pass.
I would prefer not.
I decline.
It is inevitably not going to happen.
The circumstances creates the occasion to not arise.
I ask you to refrain from asking the question.
I do not say yes.
Na.
I would rather not.
I will never accept your proposal.
Nope.
Nothing will give me the incentive to receive your offer.
I can not do that.
Don't bet on it.
There is not an intention of my approval and acceptance of the idea.
I absolutely believe that there is not a chance of this ever becoming true.