Here's a little system I came up with:
Every minute you spend being physicaly active (walking, stretching, calisthenics, wheight lifting, gardenwork, shovelglove, painting,sweeping ( washing dishes and setting the table don't count )) allowes you to spend a set amount of your free time infront of the computer. For the beginning, you can start out with 1:1, and later move on to 1:2. This will have one of two possible effects:
1. You will start being a lot more physicaly active.
2. You will significantly reduce your use of the computer.
Of course, it can also have both effects .
Similar to weekend ludite, but a bit more extensive. What do you think?