“keep voting for him for the first three ballots.”
They can’t switch to another candidate till the 4th round
The trend in second and subsequent ballots will be in Cruz's favor.
If FL is static for 3, and perhaps a few other states are static for 2 (or more), all that does is delay things a bit. Thus, if Trump does not get 1237 on Ballot#1, neither Cruz nor Trump may get it on #2, #3, #4... until #n, and with the aforementioned trend, Cruz gets the nom.
That is assuming Rule40b is essentially kept (8 states, or 5 states in the 2012 version).
Still, for this voter, November vote goes to Trump if he gets 1236+, or Cruz, if he gets 1236+.