It is possible to massage lumps of filler more flat, so they do not show. It does not technically "dissolve" the fillers. The material just flattens out and squeezes between natural collagen fibers, and is hard to find. Don't massage too hard. This can cause damage to nerves and blood vessels and can cause bruising.
If you feel there is simply too much filler and massaging will not be sufficient, injection with hyaluronidase will do the dissolving. All of this is easier to accomplish properly closer to the time of injection.
Web reference: http://www.JessicaKrantMD.com