Republicans pining for another candidate to enter the race have got to face up to the fact that there is no Jeremy Lin sitting on the Republican bench, or if there is, he's not going to get any playing time this season. Politics-as-sport analogies work great sometimes, but there is a limit. Paul Ryan recently spoke sense to the matter, and Hugh Hewitt as well. Not even rank and file Republicans think a "brokered convention" is either possible or a good idea. Speculating about another candidate getting into the race now is just an armchair quarterback's pastime, like suggesting Hillary Clinton might replace Joe Biden on the Obama ticket for 2012.
As one who sat the bench a lot in high school basketball, I know it's fun to dream about getting sent into the game with time ticking down and scoring the winning basket, but this is real life, not a movie. We go with the team on the floor, and the winner will be well positioned to take on the real opponent in the fall.