I am sorry to hear that Frank has Cushing's disease. My name is Rebecca. I am a veterinarian and will do my best to help.
There are some supplements I can recommend. Theses may help with the symptoms of Cushings, but will not suppress the adrenal gland activity like starting lysodren or trilostane would do.
Cushex drops are a homeopathic treatment you can get online. Cushex helps some dogs with the Cushing's symptoms.
SAMe and milk thistle are good for supporting the liver. There is a product called Denamarin that contains both.
Anti oxidants and fish oil would also be recommended. I like an anti oxidant product made just for dogs called Cell Advance, also available online.
For dogs with hair loss as a result of Cushing's, melatonin and flax seed oil with lignans (must contain lignans) can sometimes help the hair to grow back.
Most of these work best if done along with medication to suppress the adrenal glands, but I have had client treat with supplements alone. Since Cushing's is a very variable disease, different in each dog and with different forms (pituitary and non pituitary) the response to these supplements is not as good in some dogs as in others.
Let me know what other questions you have about Frank. Rebecca