A book of political history from 2003 called "Dark Horse: The Surprise Election and Political Murder of President James A. Garfield" (Carroll & Graf) might provide the model. Kenneth D. Ackerman tells the fascinating story of how the 1880 Republican National Convention in Chicago deadlocked, with three sets of delegates unwilling to abandon their first choice, and a totally unexpected non-candidate dark horse named James A. Garfield was nominated on the 36th ballot and then elected president.
Sen. James G. Blaine of Maine was the first major name placed in nomination, soon followed by New York powerhouse Sen. Roscoe Conkling's nomination of war hero Gen. U.S. Grant for a third term. The third major contender was Treasury Secretary John Sherman, nominated by his friend and campaign manager, Sen.-elect James A. Garfield.
The first ballot on Monday, June 7, produced Grant, 304; Blaine, 284; Sherman, 93; and a handful of votes for minor candidates. All were well short of the 379 votes needed to win.
It took two days and 36 ballots to make Garfield, who wasn't even running, the Republican Presidential candidate. This election is perhaps shaping up to have another floor fight over the nomination which hasn't happened in 50 years. The reason of course is that despite the media's much ballyhooed "top tier" and "front-runner" candidates, no one is taking a lead. The field is very crowded and the candidates are so close on issues (with the obvious exception of the good Dr. Paul) that no group or segment of the population has attached themselves to a particular candidate. and as noted in the cited article some 76% of Republicans are open to changing their mind as to whom they support. I think it is safe to say that there is no more than 5% of Ron Paul supporters who are so willing to change their support.
For those who care to keep an eye on the polls check out RealClearPolitics.com for the latest polling data compiled, averaged put into easy to read graphs. They even do the same for the polls of the early states.