Running a pusher with a mechanical fan just makes both of them inefficient. More than likely, all you will do is succeed in blocking enough airflow with the pusher fan that your car runs hot while it's moving too instead of just when it's sitting.
Your best bet is to sort out why your mechanical fan isn't up to the job, because it should be. Factory shroud, clutch fan, and a stock style fan combined with the right thermostat should be enough to keep your car cool unless you've got a much higher horsepower engine than stock. If you do, you may need more than a 22" 2-core radiator. Mixing electric fans and mechanical fans just reduces the effectiveness of both.
I run a 26" 3 core Champion radiator with a Ford Contour dual electric fan/shroud set up. Basically the entire OE ford contour set up minus the Ford controller. Works great. But I run the fans off a relay set up with heavy duty wiring (similar to what Ford did), use an aftermarket digital fan controller, and upped the amperage of my alternator (100 amps) to handle the additional draw. All things that are probably needed for any kind of electric fan set up to work properly. An electric fan that doesn't need those things won't push enough air to be worthwhile, and an electric fan that pushes enough air to be worthwhile will need those things to function the way it's intended to. A good thermostatic switch might work for some applications, but you'd still need the relays and extra juice.
