Ever heard of Sospeso or Suspended Coffee ? The idea is still fresh, but is already being practiced in Italy. You order one coffee, pay for two and donate the other coffee to those in need. The coffee stays open until someone with less money picks it up.
It is not a problem to find people who buy a coffee, the problem is more to get people into the shop who can then drink it. Whatever the case, 65 cafés in Germany are already taking part in this campaign;