Is there some further bias we can eliminate that will enable us to drag our asses to the gym even when we're feeling completely exhausted?

Yes, several. Unfortunately, the exact list is usually different from one person to the next. Here are a few I've had to get rid of:

• The idea that people who like to exercise are jerks
• The idea that it's bad to be too exhausted
• The idea that I shouldn't have to do things if they're uncomfortable
• The idea that it's embarrassing to exercise if I don't already know how
• The idea that if it's too easy, I'll be an idiot for not having done this sooner

This is less than a third of the full list, it's just the ones that come to mind right off... and I'm not really done yet, either. I lost 27 pounds last year, and expect to do a similar amount this year, but my actual habit of exercising is still pretty erratic, due to another bias which I only just eliminated. (Still too soon to tell what impact it's going to have.)