Putting words in someone else's mouth

Naturally, because it's Sefirah, and I'm not listening to instrumental music (for the time being--I may change my mind), I'm thinking about a song.

And I'm thinking that there may be some advantages to being a Jewish songwriter . . . but only if you stick to the pre-written texts. You'll never find yourself in this rather dubious position--sitting there, shtum (silent), strumming your guitar, while the other person sings about the guy/gal who broke your heart.

Maybe I just don't understand the creative process. How can you write a love song for someone else to sing?