It could work but you are causing yourself more issues.
Rule #1 in designing a surround sound system is the front 3 speakers have to be tonally matched. You just destroyed that - you're only 1 step up from the center channel behind the TV.

The quickest & cheapest way would be to remove that center channel and set the Yamaha for no center. That way it can create a phantom center channel in processing. That would be a noticeable improvement right there.

The other way is to do what golden said and get a full sound bar in there.
A powered sound bar that big (3" tall) is likely to sound like crap. And customer will not be happy with it, since it will likely be a downgrade in overall sound he's getting now.
A passive sound bar powered from that Yamaha, will do much better. The KEF linked to above would be a good start. You could also use a Triad ONWALL NANO LCR 3.0. A few other companies make skinny passive sound bars as well.