Those who wish to volunteer some of their time toward reducing existential risk and increasing our chances of a positive singularity can follow the directions on SingularityVolunteers.org.
And as a freshly hired Singularity Institute researcher, I also have my own list of tasks that, if completed by volunteers instead of myself, will speed along the delivery of the projects I'm working on: an 'FAI Open Problems' document, two papers bound for peer review, metaethics research, and more.
So if you'd like to help me out with any of my volunteer-doable tasks, please contact me: luke [at] singinst [dot] org.
Thanks!
I recommend that you find some way to hide away the flash mob mailing list- it's an idea that seems almost guaranteed to go wrong, given how easy it would be for somebody to stumble across it and scream conspiracy. It has the potential to discredit independently popular productions of the SI.
One way to do so would be to request that people send you an initial email indicating their interest, and only then send them the specific details/mailing lists.
ETA: Also, is there any particular reason the matching gifts idea is listed as an "Advanced Opportunity" instead of as the very first thing a potential volunteer should do? This strikes me as essentially throwing away money, since you say several times that people should have spent at least a few hours volunteering before they start on the advanced opportunities.