No. There is no possibility of that.
The nomination is secured by winning delegates. Romney will easily have all the delegates he needs to win on the first ballot. Period.
The trajectory for that to happen seems about dried up now...which is one of the reasons Romney went before the RNC and stated his win prematurely. At all costs the GOP did not want this to go to convention....you notice there was no outcry from any that he took this step. And clearly showed the fix is well in.
Santorum stopping just before Pa was also a strong indicator, he wasn't about to take another loss in PA and was headed for just that...it would have done in him for the career path he's determined to go...and he's still holding out his delegates for the GOP in case this does move in some unforeseen way...in order to secure Romney...and his own political ambitions