I know precisely one FBB who does this. Please suggest more! It's so hot to see the girl make her body go thinner than her thick muscular thighs, and her ribs poking out like that. Her name is Tarci Moura, btw.
I know Elena Shportun, Hülda Lopez, Morgan Rose, Tejaswini Pandit have done it. No time to search for them at the moment, though.
Veronica Valentyne's abs probably look at their best when she does a nauli. But, here is a pretty hard vacuum. The lady has some powerful abs for a smaller woman!
Here's an even better vacuum from her while standing. Fantastic muscle control!