Pretty simple really. Most schools have "commons" where students gather and talk and share ideas. How about asking community organizations to post problems/challenges they see in their communities in the commons, and ask students to submit their ideas on how to address those challenges. Hold contests with awards (I'm thinking scholarships) and lots of recognition of the student contributions. Remember, talent, like the heart, goes where it is appreciated. It we show appreciation for our students, they are more likely to bring their talents to THEIR communities instead of taking them somewhere else.