I've seen splitters like that at Tractor Supply Store and other farm stores. I would be concerned about the bearings and whether or not there would be unusual thrust loads on the shaft and other pump parts since most are made to be mounted horizontally and they don't usually have thrust bearings. If the pump isn't too expensive I would give it a shot.
You might also be able to drive it with a belt and give it a 1/4 twist.
Mark