The central question here probably is _why_ do you want PGP, or strong encryption?

What is it that the crypto is supposed to provide?

Depending on the answers you'll want completely different solutions:
- is it keeping eavesdroppers out before the flashmob happens? Short timespan, go for some sort of session key handling and AES or something like that.
- is it keeping eavesdroppers out afterwards as well? This will get tricky, depending on your paranoia levels and the timespans involved.
- is it verifying identities? Now we're talking the entire trustweb infrastructure. And here the Javascript key-generation will not do any good.