Hydrotherapy will help, we have a few dogs of 16 yrs that have been coming for almost 2 years weekly and owners have said it has massively improved and if a week is missed due to holiday etc they get noticebly stiffer.
One of our customers gives rosehip not sure what form but it is for elbow Dysplascia(sp?)
Also at crufts this year ther is a canine massage and you can attend workshops with your pet around £175 for the day but maybe they can give you excercise that will help