The 'method' attribute of form element can be set to specify the HTTP method.
<form id="ff" method="post" action="...">
...
</form>
The 'form' plugin has no 'queryParams' property, you have to add the extra parameters to the hidden input, or use the 'onBeforeLoad' event to specify the http parameters.
$('#ff').form('submit',{
onBeforeLoad: function(param){
param.p1 = ...;
param.p2 = ...;
}
});