At least for now, I'm going to have to do what that creep wants me to do, but Celestia help him if the horseshoe is ever on the other foot

Hoof

And wow, I think we have a winner for the Douchebag of the Year Award!
Look on the good side--Vinyl has at least a little bit of history with Cadance (even if only professional), and could get her support. I think the alicorn of love would realize a loveless relationship and would be disgusted by it; with royal backing, that shitstain wouldn't be able to touch their membership cards.

Alternatively... actually casting a spell to record sound would be a bit obvious, but Vinyl works with electronic music--she could get something to record sound, hide it in a good spot, and make a fake attempt to convince this tremendous asshole to quit it. If she plans out her points in advance, she could get him to confirm or admit everything he did, complete with threats to keep quiet. He'd get thrown in the slammer right away.

Let's see... extortion, quid pro quo harassment, voyeurism, power harassment, forced marriage, possibly economic abuse (not too clear on the definition here, or whether it's a part of quid pro quo harassment), intimidation, sexual misconduct, workplace abuse, and if he ever forces them into actual sex then a decent lawyer could probably slap rape charges on him, too.
And all these charges are doubled! And that's only if they're the only celeb "couple" he's created this way.