I'd agree with Gillian re the homeopathic vet and remedies.
I consulted a homeopathic vet with Cora's thryoid, and came out with what was basically and iodine solution, but it was hell to get into her, as they are drops, and I wasn't able to hide them in her food. They didn't do much either, not sure of they made her worse, or if they just didn't have any affect and the thyroid was making her ill.
Good luck with the RVC, I'd go for getting the thyroid removed.