Wire in a 3 position switch, off, on or auto. That gives you the ability to switch bilge on without the float in the equation, in case you need too.
I think option #1 in fhhuber's reply accomplishes the same thing (being able to turn on the pump manually) without adding a new switch. The only downside I see to his #1 is that there is no true "off" position, because in that example, "off" is the same as auto...
Personally, even though my boat spends most of it's life on a trailer (with the exception of a few weeks in the summer when we're at the lake), I don't want the ability to shut off the pump completely. I want it there, ready to empty my bilge if water comes into the boat. I don't want to be in the position of failing to note where the switch is and inadvertently letting the water level get too high; I want the bilge pump to come on without any intervention on my part, if needed. (I also want it to come on if I want it to....)