Want more volume on the sides and bottom of breasts - can this be achieved with breast filler?

The only filler that might make some difference is something like Sculptra. There would be at least 3 sessions 4-6 weeks apart. It would then take some time for the filler to completely build up your collagen. However, this is not permanent either. You might talk to your reconstructive surgeon about flap surgery for better volume, or exchanging your implants for something wider and bigger.

Dear booboo32,
dermal fillers are not a good option for this as they don't last long and can be expensive. Fat transfer is probably your best option. If you are considering surgery, I would suggest you consult a board-certified plastic surgeon. Only after a thorough examination, you will get more information and recommendations.
Daniel Barrett, MDCertified, American Board of Plastic SurgeryMember, American Society of Plastic SurgeryMember, American Society of Aesthetic Plastic Surgery

It takes 6-12 months for fat grafts to settle and mature; only at that time you should evaluate take of fat grafts and final result! The only "filler" for the breast is fat or local flap tissue. Obtaining 300 ml. of fat grafts, as needed for one stage of reconstraction, should not be a problem in experienced hands. Sometimes 2-3 stages of fat grafting may be needed to build needed volume. You may need to seek an expert in fat grafting, outside of breast reconstructive surgeons group. Good luck.