The thing to look out for is if romney's people want to block one of these states from counting as a plurality, they could employ a strategy where for each state Paul delegates want to use to count toward the 5 states:
they submit a certificate from the same state for romney, with the signatures of all non-Paul delegates. If the delegates for a 3rd candidate do not do the same, it effectively changes the plurality requirement to a majority.
Iowa, MN, ME, it probably wouldn't make a difference.
In a state like Colorado, santorum delegates could be a deciding factor- if the delegates are 18-16-2, and the 2 sided with romney, it would be split 18-18 and thus, not a plurality. For Colorado to count as 1 of the 5, the santorum delegates would either have to sign for Paul, sign for Santorum, or sign nothing.
In Alaska, it may work in our favor if the Gingrich and most of the santorum delegates came over, but if santorum delegates made signatures for santorum in this state so there were 3 candidates, romney would probably be able to block both.
If the RNC tweaked their interpretation of "demonstrates support from a plurality of delegates in 5 states," none of this would matter, though, and romney would be the only name on the ballot.
Another possible issue is if they say bound delegates cannot sign for another candidate because their state bylaws stipulate that delegates must do everything in their power to ensure their guy gets nominated; adding another candidate to the ballot works against this stipulation. Not sure how viable that is, but certainly they may try to use it.