AjaxFileUpload: check if file in queue exists

I've successfully implemented overwrite confirmation on classic asp.net FileUpload control following this post:http://forums.asp.net/p/1197474/2749135.aspx
Now I wonder if the same logic can (or could) be applied to latest AjaxFileUpload. What I mean is:
it is possible, maybe modifying source, intercept submitting of each file in file array, check existence server side, and, if true, add message (same as the pendingword) in the QueueContainer like: file exists please do something? (Of courseOnClientUploadComplete event is useless here since it's fired only on Upload button click)
My users asked me for drag'n'drop and multiple files upload functionality but they also need overwrite check ...
Thanks in advance for any answer to my question, negative too.