Hi,
You should be able to use the zeners then, say 15v zeners or something like that. The main idea is you dont want them conducting when you turn the coil on, you only want them conducting when the voltage jumps up to a level higher than the normal drive voltage. Because the drive voltage might vary a little you'll want the zener voltage higher than the highest the drive voltage can go.
To minimize electromagnetic radiation (assuming that's what you mean) you would want to slow up the rise and fall times of any switching signal. To do that you'd have to use a capacitor across the coil combined with a small value resistor in series with the coil. The resistor value cant be too high though or the coil wont get enough voltage, so the resistor would have to be sized according to the resistance of the coil.