Add to cart and Paypal checkout enhancement

Hi all,

I wanted to know how I can modify the checkout by paypal addition. Currently, Checkout by Paypa plugin asks for the recipient of money when configuring the plugin. But what I want to do is, to have gallery owner's email address to be the recipient of the money. So, if user X is the gallery owner,

is the recipient. And since I can have many many users, I want this to be automatically set at the time of user signup.

Can someone please help me make necessary changes?

Thanks alot guys