The Competing Frames of Clinton and Sanders
There are a lot of ways to see "us and them" in government. Most Hillary supporters see a struggle for decency and sanity between two sides: for a generation or longer, government has steadily had one side fighting for Civil Rights, for women's rights, for constraint around war, against poverty. Sanders supporters see government as owned by lobbyists and run by money, with the same corporations buying both parties. Social issues are used to keep us divided. Both these perspectives have a bit of truth, and are often the divide between Hillary and Bernie. How do you connect across the frames?
Demographics
If we want to undo BernieOrBust, the first step is to realize who is behind it. Serious activists on the Sanders campaign are desperate for people to phone bank. They post in the Facebook feeds asking people to stop posting memes and phone bank. BernieOrBust is mostly the political non-operatives, people who don't feel like they are part of the system, and therefor feel inclined to blame the whole system for corruption. These are mostly people who wouldn't be active at all in politics if it weren't for Sanders channeling the kind of energy he's had since he was young and rebellious.
Consider the messenger
Messages from the Clinton camp calling for Sanders to stop running, mixed with a message that Sanders supporters have to support you in November -- the story here is "we won, so shut up," the messenger is the opponent. Yes, there is plenty of poorly framed messaging and anger from various Sanders supporters, but that messaging is also completely ineffective or counter-productive.
The best messengers for people who think Sanders is great and Hillary is terrible are people who think Sanders great and Hillary is alright. George Takei http://www.salon.com/2016/04/28/george_takei_scolds_bernie_supporters_w… is powerful internet presence in this demographic. Once the primary is over, it seems likely that Sanders will be one of these messengers. So if you can avoid making it personal during this more heated time, avoid getting people to dig in to their positions now, and it'll get much easier after the primary.
Exchange and Fairness.
When Nader ran against Gore, many people made deals: Californian Gore-supporters would vote for Nader in exchange for Floridian Nader-supporters voting for Gore. I don't think we need such complexities now. But if you want the votes of people excited by Sanders who feel that Clinton is a good example of what's wrong with American politics even if she is on "our side" amongst the corruption, spend more time listening. Work with the Sanders supporters you know on things like petitions against Citizens United, be part of the anti-corruption and anti-money work, actively, so you are having a balanced conversation when you ask them to vote for someone they see as corrupt and only a lesser evil.
Considering getting rid of the superdelegates. Superdelegates have seemed like part of the corruption of politics, especially to younger voters waking into a system they feel very little ability to influence. The Sanders movement needs to be given some reforms: young people politically active for the first time in their lives need to leave feeling like they were listened to and that their vote (for Sanders) counted for something. Get Sanders involved, let them win this change that will impact the next primary, so people don't have to feel like the machine can never be beaten at all.
Sanders supporters feel silenced if they lose this primary. Find ways to give them back their voice and you'll mobilize that voter base.
If you want to be able to ask friends who support Sanders to give their vote to the candidate who won't show them her speeches to Goldman Sachs, what can you give them? Look for reforms to make the Democratic primary more democratic. Post about Citizens United. Be the person they hear taking the lead on reducing the corruption that upsets them most. Then you have a right to ask for their vote, rather than just hope their tactical analysis eventually lines up with yours.