Just to follow up with everyone, this worked out pretty well. The preferences file lets us set the number of cores up on the farm, but leave it normal in the project file for local rendering.
In addition, to get any benefit out of the extra cores, we had to up the subdivision cache size substantially (I think the TD is currently running with around 2GB). It's a bummer to have the total subdivision cache size set in the project file, I think it would be a lot more portable if that setting was the per-thread size. But in any case, we're getting jobs through the farm a lot faster now!
Leo