Isn't there a box where you can directly reply to the requester? What I have done in similar situations is ask the requester to email me from outside of RG (you can provide your email address in a form that isn't directly linkable or harvestable, e.g. soandso dot smith at whateveruni dot com). If the person doesn't reply in a manner that enables you to identify him and his institution, you can just forget about him; otherwise you can reply saying that the attachment is for personal use only and include a warning against distribution. If you have Adobe Acrobat Professional you can also put a large unsightly watermark across each page as a deterrent against further distribution.