Send all post variables to page

Is there a way to bypass the query string/redirect option, and just post to another page?
I would like to post to a page outside WordPress (well doesn't really matter) and populate a hidden form that I'll be auto submitting to a payment gateway. It has to be a psot thta I send to them.

Thanks.

I'm doing just that, but can't grab the first and last name fiel values. They have odd indexes.

add_action("gform_post_submission", "set_post_content", 10, 2);
function set_post_content($entry, $form){

    var_dump($entry);

	$first_name = $entry['9.3'];
	$last_name = $entry['9.6'];
	$quantity = $entry['7'];
	$product_code = $entry['3'];
	$description = 'Vehicle Sticker';
	$test = '{TESTD}';
	// Price::Qty::Code::Description::Flags
	// 9.99::1:: 001::T-Shirt::{TEST}{TESTD}{RB}
	$products = $quantity  .'::' . $product_code  . '::' . $description . '::' . $test  ;
	$address = $entry['15'];
	$city = $entry['20'];
	$state = $entry['16'];
	$zip = $entry['34'];
	$email = $entry['18'];
	$phone = $entry['17'];

	?>
	<FORM name="MyForm" action="https://secure.internetsecure.com/process.cgi" method=post">
	<input type=hidden name="GatewayID" value="15283">
	<input type=hidden name="language" value="English">
	<input type=hidden name="ReturnURL" value="http://www.autospy.org/EndofRegistration">
	<input type=hidden name="xxxCancelURL" value="http://www.autospy.org/contact">
	<input type=hidden name="Products" value="<?php echo $products; ?>">
	<input type="hidden" name="xxxName" value="<?php echo $first_name; ?>  <?php echo $first_name; ?>">
	<input type="hidden" name="xxxAddress" value="<?php echo $address; ?>">
	<input type="hidden" name="xxxCity" value="<?php echo $city; ?>">
	<input type="hidden" name="xxxState" value="<?php echo $state; ?>">
	<input type="hidden" name="xxxZipCode" value="<?php echo $zip; ?>">
	<input type="hidden" name="xxxEmail" value="<?php echo $email; ?>">
	<input type="hidden" name="xxxPhone" value="<?php echo $phone; ?>"> 

</FORM>	

<SCRIPT LANGUAGE="JavaScript">

  //document.MyForm.submit();
</SCRIPT>
<?php

}