I'm pretty sure I saw an interview with the creator of FLT where he basically said he was OK with people forking his coin. I think you should just go ahead and do it. Pretty hypocritical to attack you for forking one specific feature when FLT is based on a fork of a fork of a fork in the first place.

Thus, almost everything is imitation. The idea of The Persian Letters was taken from The Turkish Spy. Boiardo imitated Pulci, Ariosto imitated Boiardo. The most original minds borrowed from one another. Michael Cervantes makes his Don Quixote a fool; but pray is Orlando any other? It would puzzle one to decide whether knight errantry has been made more ridiculous by the grotesque painting of Cervantes, than by the luxuriant imagination of Ariosto. Metastasio has taken the greatest part of his operas from our French tragedies. Several English writers have copied us without saying one word of the matter. It is with books as with the fire in our hearths; we go to a neighbor to get the embers and light it when we return home, pass it on to others, and it belongs to everyone