How do you get more than one Paypal IPN?

I have a couple of membership sites and I noticed that Paypal only has one IPN allowed. How do you get around this issue for a script that requires the use of IPN for payment confirmation and instant activation of member accounts?

 

You can use express payment. No need PIN.

 

So basically I have to upgrade to a paid paypal service? And when you said PIN did you mean IPN?

 

send a param in your IPN url. When IPN is called, use the param to determine which site to activate, etc..