You may have more than one option. Assuming the company wants to continue performance, you might have time to make a bilateral modification adding the extension clause.  That will give you 6 months to solicit and award a new contract.

Since its 2 weeks until the end of the contract,  it is more technically sound to create a new order, preferably one with 52.217-8 included.  Again, if you invoke Far 6.301-1 or 6.302-2 for justification of a short solicitation period, you may need to consult your legal department.  Legal may also ask some questions as you seek a sole source justification.  Why was FAR 52.217-8 omitted?  Was it left out on purpose or by mistake?  Was the contract meant to end after the fifth year?   In any case, a new action with the clause should solve the problem.