How to get Paypal return URL parameters via POST

How to get Paypal return URL parameters via POST

I successfully get my token after using cURL to post the payment details
to: https://api-3t.sandbox.paypal.com/nvp
Then I redirect the user to complete the payment on:
https://www.sandbox.paypal.com/webscr?cmd=_express-checkout&token=xxx.
But when when the user finishes the payment and is redirected to my
success URL, the parameters are sent back in the URL (using GET method)
and this screws my application logic a bit. I need these parameters to be
POSTed back to my success URL.
I understand that when you send the initial parameters via a hidden form
(as opposed to using cURL), you can add the rm=2 hidden parameter to
specify that the result will be sent back using POST method after a
successful payment. Nevertheless, I cant find any equivalent to the
parameter "rm" in the NVP API for express checkout.