EntityDropDownList and AJAX ValidatorCallout

Anyone have any success with using the EntityDropDownList's RequiredFieldValidator with the AJAX ValidatorCallout control?

I suppose I could just set Required=False and then add a RFV with a ValidatorCallout manually, but I'm wondering if there would be a way to add the Ajax ValidatorCallout to the class, without messing up things for people who do not have the Ajax Control Toolkit installed.