People will tweet about your brand, no matter what, if you give them free food.
Nobody likes brands. Despite being an effective and important part of any modern marketing strategy, corporate sponsorships are lame as hell and "branding" has become a dirty word. And putting hashtags in your tweets to support a new product or service is basically like publicly shouting out that you're a little kiss-ass. These days, people care about one brand: their personal brand, and they aren't going to fuck that up by tweeting about your stupid new ad campaign...
Unless you give them free food.
Give a man a free sandwich and he will literally be like: "I'm a #SubwayGal! Enjoying a sandwich at SXSW at the Subway Sandwich Salon. #EatMe #Hehe"