validate ajaxfileupload "hasfile"?

Hi All: I have a webpage with 4 regular fileupload controls, and validation to prevent the page from being submited unless all 4 fileuploads are populated.

I use a customValidator both client-side and server-side to validate that all 4 fileupload controls have files and have the appropriate file extensions.

In my client-side validation I used logic like:

<script type="text/javascript">
    function valUpload(source, args) {
        var pdf1 = document.getElementById('<%#fupPDF1.clientID %>').value;

        if (pdf1.length == 0) {
            	source.innerText = "Attach file for upload 1";
            	args.IsValid = false;}
	else
		{args.IsValid = true;}
	}</script>

and server-side like:

If fupPDF1.HasFile and fupPDF1.fileName isnot nothing Then
	e.IsValid=true
Else
	e.IsValid=false
End If

I want to replace these fileuploads with ajaxFileUpload controls. I see that I can restrict each ajax control to a single file, and I can validate the file extensions from within each control. So far so good!

What I'd like to do is validate each control to make sure the end-user has uploaded a file, before submitting the form. Is there a way to do this within a customValidator?