The appropriate answer is not as simple as "hitting it". The first thing to do would be to appeal to her sense of self-worth and to ensure that she feels that she is beautiful, regardless of her weight.
Only then can you tend to the task of getting her to realize that her weight makes her a ticking time bomb in regards to her health. Support her in getting her stomach stapled. Gently persuade her to get a personal trainer and a makeover.
Finally, once she loses about 70lbs and undergoes some plastic surgery to get rid of the extra skin that comes with such drastic weight loss, fuck the shit out of her every opportunity you get. Make sure that she puts you on her will first though, so if she suffers a heart attack or stroke mid coitus that your efforts do not go unrewarded.
That's how I would do it.
__________________
|