In theory you wold have to create a new class by extending the "dojox.data.QueryReadStore", in the link you posted have an example for doing exactly what you want. See if you get it now(changed a bit):
dojo.require("dojox.data.QueryReadStore");
dojo.declare("custom.MyReadStore", dojox.data.QueryReadStore, {
fetch:function(request){
//append here your custom parameters:
var qs = {p1:"This is parameter 1",
q:request.query.name
}
request.serverQuery = qs;
// Call superclasses' fetch
return this.inherited("fetch", arguments);
}
});
So When come to create the QueryReadStore you actually create a object with the class you defined. something like this:
var queryReadStore = new custom.MyReadStore({args...})
Explore the request parameter passed to the function to see what else you can do.