Well, if you can include wheat in your 20% (for now) and it doesn't bring on other cravings, I think Mark intended this to be something you could do for life and not say "well I blew it now I might as well wait until Monday (or the 1st of the month or whatever)". I have a "naturally skinny" friend. She cannot gain weight. But she does watch what she eats in an attempt to stay healthy for life. But, if she opts to eat something that doesn't fit into her plan, she literally savors every single bite, considers it part of her plan right now, and gets back to what ever she would normally do next. I often use her as an example of how I want to view food. Mostly as a life giving force, and sometimes something to savor.
Guitar or voice lessons sound like a fantastic way to use that money. Take the emphasis off of diet and food and onto something you truly enjoy that will help to "round you out" as a sort of Rennaissance Woman!