All they have to do is seriously play up the "Giant of Lannister" bit. Have her say it during the trial, make the laughter a complete uproar, make even Tywin laugh before turning cold, show the look between Tywin and Tyrion, completely break the father/son bond.
Then Tyrion goes to Tywin's chamber, Shae apologizes, Shae begs forgiveness, Tyrion accepts and embraces her because what else could she do? Then she says "My lion, my giant of lannister, I'm so sorry." And that's when he grabs the chain.
Done. It fits a perfectly disgraced Tyrion to a "t". It's not like Tyrion is afraid of hurting people, anyway, doesn't anyone remember the singer and For hands of gold are always cold, but a woman's hands are warm...?