I have been able to get the Dynamic plug in to work flawlessly when triggering based on a URL variable.
You can see it in action here on one of my radio station websites: equest.php?var=equest
It uses the "var" variable defined in the URL... upon submitting request, it redirects back to the same page with one change to the URL variable and that completely changed the plug in it pulls showing that the information was sent.
Totally love this extension!