You can't. At least, not all at once.
What you can do is have the form be submitted to a processing PHP script which then uses something like [man]cURL/man (or even [man]file_get_contents/man if you create your own stream context) to re-POST the data to whatever PHP script(s) you need. However, if these scripts are located on your own website, then it would be far easier and more efficient to simply do all of the processing that the separate scripts do in one (or perhaps modify those scripts so that they could be include()'ed locally).
