I would do it like this: <dataset name="ds" request="false" src="http://www.../sr.php" />
and then your button code would be:
<button text="Submit" onclick="sendit()">
<method name="sendit">
var d = canvas.datasets.ds;
var p = new LzParam();
p.addValue('qs', 'stuff' ,true);
d.setQueryString(p);
d.doRequest();
</method>
</button>
(Warning: this is untested email code.)
HTH,
Dave
