I know a few joint degree programs accept the LSAT instead of making you take the GRE. The only one that I'm really interested in is Virginia's JD/MA in history. It's a three year program, costs nothing extra, and accepts the LSAT.
Congratulations! Duke is a great school. One of the most underrated in the T14, imo. The history of the school alone makes it worth attending. Good luck on the rest of your applications!