I think if we’re not going to go with a poem, we should make it as easy to follow as possible. The audience is only going to hear this once, and there’s a rule of thumb in film that you need to repeat something three times for the audience to retain it automatically.
I agree that keeping iambic pentameter would be good even if it doesn’t rhyme; again, that was a technique Shakespeare used for his characters from the nobility. I’ve got some ideas of my own, I’ll mess around with something tonight and see how it goes.