Pmiller, sorry to hear about your cavalier....
Have you let the breeder know about the Patellas they also may have some suggestions as to what you can do...
Firstly, keep the cav away from stairs... if required carry them up and down the stairs..
Dont let him jump on the lounge, or really jump on anything...
Patellas can be a problem and they may need sergical intervention, but not always, if you are not heepy with what your vet told you then go see another one.
Sometimes building up the muscles around the patella can correct it... I would try some hydrotherapy to strengthen the muscles.
Good luck and keep us updated.