What if Romney uncharacteristically decides to pull a 1956 Stevenson-lite? Let's say Romney decides after all his vetting that there are two or three people remaining from his short list and that he has no obvious preference between them. Submitting his his picks to the convention for them to decide would certainly create some buzz for the boring ritual that conventions are these days.
So if Romney submits say Portman, Ryan, and Jindal to the convention, who do you think wins? Does it go past a first ballot?
That would be an interesting thing to do, but in a convention like the 2012 Republican one, where a lot of Paulist delegates will be
tolerated, it's doubtful. Maybe Romney could hold a faux-election; send out ballots to Republican primary members with the names of the Veep frontrunners and ask them to vote and send the ballots to the local GOP headquarters, where they would be counted. But I feel like a VP election is too exotic for Mitt Romney. He will quietly come to a decision with a few close advisors (ie, his family and Beth Myers), and then announce it after carefully considering the timing. For all we know, this has all already been done and the announcement simply hasn't happened yet.