Oh, I got a treadmill for the same purpose. I rigged a table top over it and I type at it or I watch TV from it. I set it on something like 2.0 and just walk slow while I type or watch TV. It's not my workout, but it's definitely great extra movement.
There's no motivating, there's only doing.
Perhaps you can not allow yourself to watch your movies unless you're moving on the treadmill. Just keep it simple. My problem is making it too hard. I've got it in my head now that it's not good enough if I don't make it to 3+ miles, but that's just stupid. It's mentality like that that messes up a good thing.