Butt augmentation for a flat butt?

In your particular case, it sounds like you may be a good candidate for a Brazilian buttock lift or fat transfer. This involves first performing liposuction fat from the unwanted areas, such as abdomen and lower back, then transferring or injecting the fat into the desirable areas, such as the buttocks. Not only does this create a fuller appearing buttock area, but it also decreased the size of the nearby areas such as lower back, sides, and abdomen. This creates an overall aesthetically appealing gluteal/lower back/hip area.
A board certified plastic surgeon experienced in this type of surgery will be able to evaluate you to determine if you are indeed a candidate for this procedure.
Best wishes,
Dr. Bruno

Thanks for the question.
You've hit on one of the newer trends in body contouring, fat transfer. As a plastic surgeon it hits on concepts that we find very positive - move tissue from an area people don't want it into an area they do.
This technique has significant benefits over implants (reduced chance of infection, capsular contracture, implant extrusion, pain, etc.)
In our San Francisco area practice we perform a careful analysis of the areas you wish fat to be removed from and make an assessment of how much volume it will take to meet your goal.
Be sure to find a board certified plastic surgeon to help you with your needs.
I hope this helps.