I have created my own conditional validation attribute to validate my MVC model on both the client and the server by inheriting from RequiredAttribute
and imple
I had a similar problem where I wanted to revalidate a datepicker field using jquery validate and jquery ui. This post helped me figure it out.
The key, is just add a callback to the valid method for that selector. Something like:
$(".requiredif").change(function() {
$(this).valid();
})
You should check out Foolproof Validation. It does what you are trying to do without you having to roll your own.