Assuming that the seizures are being caused by hypoglycemia and not vice versa, then the real question is what is causing the hypoglycemia? Adult Yorkies do not have low blood sugar sufficient enough to cause seizures with no reason. Maybe this link can help. It addresses hypoglycemia in adult dogs that is not caused by epilepsy. I think that you are doing exactly what you should be but its important to find the underlying cause.
http://www.canine-epilepsy.com/under...l#anchor700068