Nothing on the build side of things at the moment. My current idea is to use the two S3D capable projectors and hide the third turned off to enable NVIDIA 3D Vision Surround. That'll allow me to run 3DVS on just two projectors for the setup. I then setup NTHUSIM for dual-projector and scale the triple resolution to the dual-projection. I'm pondering setting the triple resolution to 3072x768 and projecting that as 2560x720. NTHUSIM's bicubic scaling should make it look good regardless of whatever I do. It's not ideal but it'll work. Alternatively, I'm pondering selling my three EX525ST and getting the third projector that way, but as is this screen design is currently configured for dual-projector layout.
Experimenting with the GT720's today it looks like setting "High Altitude" mode on the fans might compensate for portrait rotation, so an alternate setup could be 3x1P 2150x1280 with 16:10 AR set on the projectors to scale as 2400x1280. Either way it goes these are pretty odd configurations just to get S3D function on a curved screen. The advantage of 3x1P is really short throw and a projection with 1280 pixel height.