I'm an Obama supporter, but I found the argument expressed in the latest New Rules by Bill Maher to be a very persuasive one:

If voting can destroy the Democratic Party, then the party isn't very democratic. Democrats need to stop freaking out about how this long primary battle by two popular candidates needs to be settled yesterday...

Democrats, your task is not just to choose between this pair, it's to grow a pair... What is so terrible about a long, drawn out contest?

The move by Obama surrogates to call for Hillary to drop out does seem like not only a miscalculation, but a fairly wimpy move.  And Obama's quickness in saying she can stay in as long as she likes suggests he knew that sort of talk might rub a lot of people the wrong way (especially those Democratic voters who haven't had the opportunity to vote yet).

Still, the idea that the nominee should be decided upon before this battle ends up at the convention is a very reasonable one.  And for either candidate to indicate an earlier ending (with less blood spilled) could be possible would reassure a lot of Dems who are starting, as Maher said, to really freak out about this.

For Obama, directly pressuring Clinton to quit- or having his surrogates do so - has pretty much already proven to be a backfired strategy.

So instead, he should take a page from Hillary's playbook.  When she had the opportunity to try and make him look weak and afraid to speak in detail about his ideas, she jumped at it and challenged him to more debates.  She basically said, "Okay, if you really have solid positions and not just great speeches, then I'm calling you out - I'm going to make you back it up!" 

He should take a similar approach in suggesting a happy ending to this fairly bitter fight, and instead of saying what she should do, say what he would do.  I've seen Hillary supporters on CNN expressing confidence that she'll get a big enough win in Pennsylvania to turn the tide and win not only the popular vote but also the pledge delegate count by the end of the primary/caucus season.  In those talking head debates, Obama should have a surrogate there to hint:

"Well, if either candidate wins both the popular vote and the pledged delegates, s/he should concede and withdraw from the race."

Obama should not be calling for Clinton to quit prematurely, but indicating that either candidate - including himself - should abide by the will of the voters after they've all had their say.

I guess there would be a risk of sounding like a loser, but for him to put his money where his mouth is and call for her to do the same seems to me to be a more high road approach than just having people call for her to drop out now.

It's a harder position for her to counter without looking like she's willing to dismiss the will of the people, and since the odds are so heavily in his favor at this point, it's a fairly low risk gamble.