He who hesitates is lost.  On the other hand, remember that treaty benefits aren't always recognized by state income tax laws.  I hope you're in Texas or Florida.  Well, no, that sounds like a death sentence.  I hope you're not in California, where I think there was a question a while back about taxation of some country's Social Security benefits. 

If it makes you feel better, attach a pdf explanation to the return, since no one at IRS reads attachments but it might save some research by the next practitioner who gets this client.