In many cases an employer may have an agreement with the insurance carrier that there will be 100% participation. In those cases often when an employee provides proof of spousal coverage, the insurance carrier will accept that as meeting the 100% participation agreement.
Have you asked whether or not proof of spousal coverage will be acceptable? If not, go directly to the insurance carrier. Give them the group and policy numbers - they HAVE to have that to give you an accurate answer - and ask them directly whether or not there is a 100% participation clause in the contract and if so, will proof of spousal coverage be accepted. If the answer to both questions is yes, ask them to fax or e-mail you something to that effect that you can show the district.
If the answer to either question is no, you will need to contact your state insurance commission to find out if you can be forced to pay for coverage you don't want under your state's regs.