Custom asp.net mvc 3 jquery.validate.unobtrusive

I am converting a site from asp.net mvc 2 to asp.net mvc 3. I am wanting to use the built in validation in mvc 3 which uses the jquery.validate and the jquery.validate.unobtrusive. However on my old site I was already using jquery.validate and added custom method for validation that I would then call when a drop down was changed.

I need to be able to:

1. Register this method.
2. Call only when the dropdown is changed.

Here is my code for this on my asp.net 2 site.

//add class to the html element
$("#ClientId-input").addClass("validClient");

//create the method "validClient"
$.validator.addMethod("validClient", function(value, element) {

    //get the actual value in the input box
    var _value =  $("#ClientId").data('tComboBox').value();

    //get all the items in the list
    var _items = $("#ClientId").data('tComboBox').data;

    //set the value to return
    var _retVal = false;

    //loop through the items if the selected value equals a value we are valid
    $.each(_items, function(index, value)
    {
        if(value.Value == _value){
            _retVal = true;

            //return false in the loop to break.
            return false;
        }
    });

    return _retVal;

}, "Please choose a Client from the list.");


//Assign the rule to the validator
$.validator.addClassRules({
    validClient:{validClient:true}
});


//this is called when dropdownchanges
function ClientsChanged(e)
{

    if($("#ClientId-input").valid())
    {
        //do work here
    }
}