Amazing that no one has mentioned High Speed Sync! (HSS) where the camera will sync at more or less any speed you like! I've had the 5D MkII sync at 1/4000th. OK there are are downsides, like the lack of power, and the fact it makes the flash gun work hard, but it is a feature included just for this specific purpose, and you can always use multiple guns to up the power if you need.
Alternatively there's static light which needs either mains or a generator, but will overcome daylight. And as a slightly different approach, this is a problem associated with focal plane shutters, so get an adaptor and a lens with a leaf shutter, set the DSLR in bulb mode and then fire the leaf shutter which will sync at much faster speeds.
Or you use a tripod expose the sky, move the subject in, and expose for them & either do an HDR or cut & shut.
Sometimes a camera will just not be capable of doing what you want, and you have to be prepared to do a work around.