How to force PayPall just after "Give me a site" with supporter for a free trial

Hi, What I want to do is this

On the sign-up form have (granted by the supporter plugin) the options of:
---Do you want to be a supporter? "I'm interested" or "Not now"
NO-MATTER WHAT the newcomer chooses they have to immediately be taken to PayPall where they must fill out their info. Now.
If they chose "I'm interested" they get charged the appropriate amount.
If they chose "Not now" they still have to fill their info BUT, get charged AFTER their predefined free period is over unless they cancel.
They are given access to their site after and only after the have filled out their info to PayPall

I think this is possible and have seen a thread in here someplace but could you please help anyway?
If yes, how. If not please consider it as a request

Thank you