Keeping miles is easy. Just join their ‘dining’ program. You join the program and attach any credit card you wish to it. Then you charge anything at one of those restaurants on that credit card and it activates your account on that date. You get equivalent miles (1:1) and it protects you from losing your miles for another cycle.
I go to a nearby Burger King and charge a small fry once every 6 months on my credit card (June and Dec) to protect my miles. Very easy.