Hmmmm, now there's an interesting find! So it turns out the Elves have been feeding Frodo and co. the Middle-Earth equivalent of spacecake?
Galadriel: "Far out, dude!"
----------------------
All sillyness aside, I'm not sure there are many hints that the Lembas had that much of an effect on Frodo and Sam. Upon rereading Frodo's behaviour it doesn't seem like he's longing to be with the elves, but instead his anguish seems to be caused by his addiction to the Ring and his feeling of guilt for having 'failed' his quest. It is also important to note that Sam is not experiencing any longing for Aman at all, even though he had the same kind of exposure to Lembas as Frodo, though it may be that the more earthly Sam would be less likely to be influenced by the lembas than the more spiritual and 'Elf-attuned' Frodo.
Damn Elves and their hippie ways.......