[jaggederest]

From what I understand, behaviorally there are two systems. There's active management, i.e. exerting willpower, and there's habitual behavior, i.e. doing what you usually do.

In the same way that "You" are not a monolithic entity, "You" don't pay attention to everything - take the old "think about your breathing" troll, which causes a redirection of attention to an otherwise autonomous function.

In this world, the role of "willpower" is in habit formation - doing something routinely enough that you train 'yourself' to do it automatically. So exercising this ability can help you train yourself to do it more easily - you're meta-training yourself to train yourself.

But the active exercise of will is by no means energetically free, and that's the origin of the original paper's hypothesis. I'd guess that this exercise of will is not especially amenable to alteration beyond gross physical trauma, but I don't think it has much to do with blood glucose.