Personally I feel like crap if I don't exercise, I don't know how people who don't exercise motivate themselves to not exercise.
I am blessed with the Don't Exercise gene. That's how I do it.
In my experience, the trick is to not exercise. Get a hobby that involves physical movement. I collect such hobbies, and the only time I actually exercise it's because I've pulled a muscle or something and need to do rehab exercises.
You probably won't pull your muscles as often as I do if you get yourself some safer hobbies than the ones I've picked, but hey, no accounting for taste, right?