Let me know if you think www.flashvolunteer.org might be of some use. We are a Seattle-based nonprofit tech startup focused on real-time volunteer opportunities. We also have a mobile app (Seattle only right now, but could easily be opened up for Baltimore) that could facilitate these sort of events. You can check it out here: http://bit.ly/XTd45K.
Let me know if you'd like to chat,
brad [at] flashvolunteer [dot] org