Good question. We thought about what we should do after YC.
Post rejection, we waited a few weeks until we had some pretty good traction stats, and then sent an email to PG asking they reconsider us. We got an email back saying they don't change their decisions because they wouldn't be able to scale that way.
In this case, we didn't think the best thing was to do flashy techniques, based on what we've heard about PG. Depending on where our startup is, we may apply again next batch. We're applying to other incubators right now too.