PayPal Integration, how would I define the receiver account?

I'm working on a very small ecommerce software that allows users to put their products up in order to get customers to see them and buy them.

I would like to offer the paypal option and therefore working on creating a module for it.

I started out with this:

http://sanwebe.com/assets/paypal-express-checkout/

Which got me started pretty good, but my "problem" is now that the receiver is automatically the API username?

That is what i can see in the RECEIVEREMAIL parameter value from the response that I get from paypal after an payment.

I would like the receiver to be my users email which i got in the db. So that they get the payment directly into their account.

So I would need to specify the email/paypal account email somewhere in the code?

Hope somebody can explain me how this would be done, I can understand it may not be possible doing while in sandbox mode - but can someone clarify that API information is one thing and receiver is another?

Update: I just found out I can have

&PAYMENTREQUEST_0_SELLERPAYPALACCOUNTID=receiver@email.com

in my call to PayPal. Although this still does not work, it still shows the dev. api username.

Here's another with the same question, but left unanswered:

Doesn't the SELLERPAYPALACCOUNTID work in the sandbox?

from PayPal Integration, how would I define the receiver account?