There is no way around the S code -- you should be getting an ABN signed... billing J3490 is unethical.
The S codes are used by the Blue Cross/Blue Shield Association (BCBSA) and the Health Insurance Association of America (HIAA) to report drugs, services, and supplies for which there are no national codes but for which codes are needed by the private sector to implement policies, programs, or claims processing. They are for the purpose of meeting the particular needs of the private sector. These codes are also used by the Medicaid program, but they are not payable by Medicare.