Note: Without actually doing it, there is no way to know if this would even workout in a day-to-day usable way. But in theory, it should work. Just doesn't make sense.

Any insight as to why the customer just will not allow additional speakers anywhere (soundbar, in-wall, in-ceiling, bookshelf, etc.). When they already have a set of in-ceiling speakers installed in the room?
Was it they had them put in when the house was built but now regret it, because they don't like how they look? But want to use them somehow because they are there?

With custom options available such as invisible speakers and custom built soundbars to match the TV and/or decor, I'm guessing the customer doesn't want anything showing but is to cheap to pay for a custom solution.
But probably has a $13k SubZero fridge in the kitchen. With a $12k Thermador stove that they never use. LMFAO!