PayPal IPN Pass around

I want to create a paypal button and have the IPN pass through LeadFlowPro, so I can add the orders to my LeadFlowPro to track everything.

They have a IPN Passthrough. would it be best to leave the IPN directly to the return url, but send the THANK YOU Page directly to the IPN passthrough, since they will return the query string sent with them back to the end url, so everything paypal sends to the LeadFlowPro, they would return to the return URL, I could put in there.

would that work?