How to set manually parameters for ajaxRequest()?

[Igniter]

I develop custom filtering, and I need somehow post values to be filtered by, while ajaxRequest(). Any ideas?

[Igniter]

var grid = $("#MyGrid").data("tGrid");
var originalUrl = grid.ajax.selectUrl;
grid.ajax.selectUrl = originalUrl + "&filterQuery=" + query;
grid.ajaxRequest();
//grid.ajax.selectUrl = originalUrl;

The working one code (for now).