You totally can. Map your route to go around the "biggest hills". Topography maps available on Google maps and such.

You get more torque to the rear wheel on a Single Speed / Fixed. It will make hill-climbing easier. A lot easier.

I bust up hills on my SS so much faster than on any of my geared bikes.

It's nice to have the gears when you need em' though, like on long rides and super duper hilly terrains in the countryside.