I am a provider that prefers a more permanent solution than Sculptra (Bellafil), but I also use Sculptra too. Regardless of the product used, you should know the hard truth about using fillers to contour the buttocks. Simply put, it takes far far more product to affect the smallest changes than you realize or that any provider I know performs. It typically takes hundreds of cc's of fat to make changes to the buttocks, and that volume of material would be no different for fillers. So, the TRUE answer to your question would be HUNDREDS of vials of filler. Don't believe me? Then go get 20 vials per cheek (40 vials total and tens of thousands of dollars). Be sure you get good before photos from multiple angles, and then again after photos at least 2 months later. You will quickly realize that I speak the truth. You appear to have already had liposuction and fat grafting, and if you want to enhance this you should do it again; it's always the best (and cheapest!) way to go.