In a serendipitous encounter with an experienced programmer (at a bar), I learned that the question I ask has no easy solution; what he suggested, in fact, was what I have long resolved to doing, which is
1) ensuring the files are uploaded to a private directory, unable to be accessed by anyone but myself and insulated (to the best extent possible) from the rest of the server in terms of malicious code, and
2) sorting through these files as they come in, 'approving' them on a case by case basis.
That being said, I was wondering if anyone could advise me on the best way to accomplish either part of this; if I remember from my "Beginning pHp" book, the former has to do with .htaccess, a realm with which I have no experience. In terms of the latter, if anyone has a better suggestion than trying to open each file on my personal computer, I would be more than happy to hear it.