So... when your willpower is all gone, you continue doing the activity with... what?

Although, I have no desire to do it, I force myself to do it. So it can be argued that it is till your willpower to do it. But this willpower is not for the activity but for the sheer reason of doing a little more of an activity. Thus, this willpower is orthogonal to the willpower of doing the activity.

An article in the NY times is an interesting read, mentions something close to my technique.