OK, how about really easy stuff, like systematically emailing researchers involved with synthetic biology and trying to convince them to reconsider their choice of field? Feels like ideally we would get someone who knew stuff about biology (and ideally had some level of respect in the biology community) to do this.

Systematically emailing researchers runs the risk of being pattern matched to crank spam. If I were a respected biologist, a better plan might be to

1. write a short (500-1500 words) editorial that communicates the strongest arguments with the least inferential distance, and sign it
2. get other recognized scientists to sign it
3. contact the editors of Science, Nature, and PNAS and ask whether they'd like to publish it
4. if step 3 works, try to get an interview or segment on those journals' podcasts (all three have podcasts), and try putting out a press release
5. if step 3 fails, try getting a more specific journal like Cell or Nature Genetics to publish it

Some of these steps could of course be expanded or reordered (for example, it might be quicker to get a less famous journal to publish an editorial, and then use that as a stepping stone into Science/Nature/PNAS). I'm also ignoring the possibility that synthetic biologists have already considered risks of their work, and would react badly to being nagged (however professionally) about it.

Edit: Martin Rees got an editorial into Science about catastrophic risk just a few weeks ago, which is minor evidence that this kind of approach can work.