I don't personally recommend that at all but if you feel like you must do something, please work with a reputable and licensed cosmetic surgeon who has experience in that area. There are some. You can find them by searching the internet. And they won't use silicon injections but will do something similar to breast augmentation, using silicon or saline filled forms. The problem I see is that either of those types are subject to breakage even in the breast area. I would think the risk of breakage is even higher on the hips.