I've been responding to questions via PM, but for the public benefit, here's a general description of my scholarship negotiation:
I wrote a letter, maybe three quarters of a page single spaced, and didn't even mention other schools at first. The paragraphs, in order, were basically:
-Thanks for admission and scholarship, affirm sincere interest in attendance
-Indicate concern about the cost of legal edcuation. Here I included a rough estimate of my day-after-graduation loan principal, and a calculation of the interest I would have accrued before I even started working as a lawyer
-Why this is a problem, given that I have no intent to pursue Biglaw and want to work in public service
-Brief explication of my public service background (I was a Peace Corps volunteer and I've always worked in nonprofit and government roles for my professional career so far)
-Final thank you and invitation to reply or call me to discuss further
Shortly after I sent the email, they responded to ask explicitly whether I had competitive offers from peer schools. I responded with two of my current offers - a full ride + stipend from my hometown flagship and the full/10/10 from Colorado (neither really a "peer school" to WUSTL, but I was seriously considering both) - and indicated that I was negotiating scholarships with Colorado, UW, Georgetown, and Northwestern. I also indicated that I still had applications outstanding at a few other schools in the T14.
This was all about two weeks ago, so I imagine they had scholarship negotiation meetings in the meantime before deciding to up my grant. Also, for those of you who haven't seen it yet, MS9 & Co. posted a great blog with tips for negotiating scholarships.