He should help his younger supporters understand that a progressive movement is possible only if they get involved in local politics and support candidates (or run themselves) who are committed to the ideals for which he claims to stand. He can point to places like Berkeley and Eugene to illustrate that it is possible to make a difference at the local level. He can point to how same-sex marriage would never have become the law of the land if progressive communities and states didn't push if forward first (if not completely).
I don't know that he will do that, however, because his model is based overthrow. I hope, though, he has learned something himself, including that every mass protest movement of late (his, OWS) has failed to force direct change. Politics is local--learn how to work within that system to be the change.
Not for nothing, the narrative that he was undermined by the media is flat out false. I watch network news programs, and every one of them had him on, asked him softball questions, and included him positively in their recaps of campaign news. His name was front and present as any other candidate, and it without a doubt helped get his message out. He lost because he did not present a sufficiently compelling case for himself or his policies, same as many other candidates of the past.