I designed various versions of valving to do this, as it is one of my many projects. I tried to keep it as simple as possible. I will try and find my sketches if you don't have any luck.
My little Steiner tractor has a V blade and I don't like the way they operate one side at a time only. For that one, I'm putting a pushbutton, light and timer circuit. I can press the button to toggle the valve on and off and the timer shuts it off, because probably the solenoid valve is not designed for continuous use. But this way, I can operate the Aux valve without simultaneously having to push the button.