[Wyrd bið ful aræd]

With few exceptions, these delegates are bound to Rubio on the first vote. This skulduggery would only come into play if Trump doesn't reach the requisite number of delegates outright, which is unlikely.

The other possible scenario is that Rubio formally ends his campaign, instead of simply suspending it as is the current situation, in which case the delegates are free to vote for whoever the hell they want. And since delegates in most states are assigned instead of chosen, there is a good likelihood that many of them don't like Rubio anyway. In any event, they are not his to "release to Cruz." He has zero authority over them.

[StAnDeliver]

"The other possible scenario is that Rubio formally ends his campaign, instead of simply suspending it as is the current situation, in which case the delegates are free to vote for whoever the hell they want."

Never happen. If he does he cannot use the remaining funds for his now-certain-to-be-contested Senate race, nor attend ur-election grayzone PAC/GOPe/Convention doings using those funds. And Foam Boy likes to fly downlow/underradar/privately...