Seeing how the song lyrics form the entire premise of the film, complete with events and characters, OMB seems fine to me here.

Dale Launer didn't just wake up one morning and thought to himself: hey, let me write a script about a guy who gets some kind of "love potion" from a Madame Ruth on Thirty-Fourth and Vine - no, there's hardly an original thought there, it all comes straight from the song. If this all sprang from the mind of Dale Launer, then he'd deserve sole writing credit. But it didn't: it's a film based on an existing piece of material. Whether that existing piece of material is a book, a play, a song, an idea even, shouldn't matter. To me, this is exactly what OMB is.

It's been a l-o-n-g time since I watched this and I remember very little of it, but if it is a close to the song as T!M says, then I can accept OMB.

However, I wouldn't go quite as far as T!M when it comes to the type of souce that's accepted. "Adapted from another work" is what the rule says. I would not call an idea a work. And to me, "inspired by" sounded like just an idea. But I'll buy that in this case it's indeed more than that.