Not sure. Maybe a fully-fleshed out profile could be visually appealing? Or the website could announce that the profile is only 80% complete (like how OKCupid and LinkedIn do it).
I have another idea. What about finding a small group of colleges that compete with each other, filling out the profiles for those phd people, and then writing a blog post about it and sending it to the colleges?
Maybe the colleges will use it in marketing material or a blog post. Free publicity for everyone involved!
Then, whomever is reading the college's blog because they care about that kind of stuff will be compelled to claim their profile.
Or a big "claim my profile" link?