I've got hills like that too, and I also don't have a cadence counter thinger. My solution was to put my watch in a place I could see the seconds tick by while riding and time it so I was pedaling 60bpm, one rotation per second. Once I figured how that felt, I knew that I had to pedal 1.5 times that fast to reach 90bpm, and now I try to keep it at least there, especially on my hills. You don't need to spend the money on computers if you don't want to and won't use it for much.

Just enjoy the ride and the freshness at work.