Hi!
I'm afraid this isn't going to work, though I really hope I'm wrong.
Here's why.
TMAU isn't caused by choline per say, its caused by excess trimethylamine produced by gut bacteria from choline. So eating a lot of niacin might effect the ammount of choline that goes into your system by absorbtion, BUT its not likely to prevent your gut from making trimethylamine from the food that you eat.
I'm pretty sure I also have TMAU and I have read EVERYTHING about it on the web, both scientific and non-scientific.
But as I said, I hope I'm wrong. And ofcourse I will give b-3 a go.
Take care.