Starbucks should give loyal patrons their own personalized mug, to use and keep at the store. The store would clean it for you between visits.
Picture a German brew house, with ornate personalize steins on the wall.
You'd get loyal customers, word of mouth from people showing off their special mug, and a chance to be genuinely green.
Even better, try what Munich's Hofbräuhaus does: reserved tables for regular guests. This is how you get raving fans.