Is there a way to manually initiate client-side validation?

I'm converting a project over to using jQuery's ThickBox control, which displays a modal dialog box.  In a particular dialog box I have a number of input fields, some of which have RequiredFieldValidator controls connected to them.
Here's the dilemma I have: When the Javascript required to use ThickBox with ASP.Net is connected to the Submit button then the dialog box closes - every single time.  The problem with that is that the Validation becomes a moot point, because even if the data is incomplete the dialog box still closes.  When I remove this Javascript then the Validation does run normally but if everything is fine with the entered data then the dialog box never closes.  So I'm in a bit of a paradox.
I've thus got to wondering if there's a way that I could force the Validation of the ASP.Net validator controls to execute programmatically via a Javascript call?  Depending on what was returned from this call, I could ...