If you connected a separate valve to the remote connections, it would have to be an open center valve. The tractor remote control would be in an "on" position for the fluid to get to the new double valve and this new valve would control your blower rotater and deflector cylinders. With the tractor remote control lever in the "on" position, you'd have no 3pth control. I don't if you ever noticed but when you're using the bh, the 3pth is dead. The 3pth only works when the remotes are in the neutral position.
If you have two sets of rear remotes, you're allready good except for some hoses to the two cylinders of the blower. If you only have one, then it may be easier and cheaper to add the second remote. Use both to make your two cylinder adjustments and when the remotes are back into the neutral position, the 3pth is operable.
Another member might know of a way to use the power beyond circuit but that I'm not familair with.