as mentioned, he can use it as a regular ticket for 1 day but disney doesn't do combining or refunds on tickets. There is a ticket priority so if there is a specific day you know your not park hopping, stop at guest relations and make sure that 1 day ticket will be used and use your 6 day hoppers for all the other days.
Of course, have him talk to work as ask if he can just reimburse the much cheaper add a day of tickets he already has. then work only has to pay the $15ish for the upgrade and you get 7 day park hopper tickets.