And you don't need to install it upside down; since it will be away from the strings, magnetic polarity is irrelevant, you can simply reverse the wiring.
Yes, the magnetic polarity is irrelevant, but....there are details on how pickups are wound (the ground lead is often the "end" lead (so it shields the other windings) making the hot lead the start lead) that help with electrostatic buzz issues. Yes, you can reverse the coil on a standard pickup, and you'll have less hum than without it, but if you flip it (install it upside down), because of those details, it works even better. Do you want your bass to be "less noisy" or silent?