As far as I know, "change" is not an option, since in an effort to eliminate the social pressure of "I better pay something since all these people are looking" effect, he provides a locked metal box for you to slip your envelope into at the end of your stay. Also, he mentions enjoying the food drink and convenience all week and then dropping a $20 in the box. And there's a paypal link on the restaurant's homepage. I could pay from my desk, then drive over and eat and drink.
But today was McD's.
High grub factor. taste*convenience/$