You can add the dining plan to the reservation. In order to get it for only 5 of the nights, you have to ask the owner to have the reservation segmented first and then add the plan. This is something relatively new as you had to get it for all the nights before now (unless you did a split stay).
In addition, since the plan has to paid for when it is added, at least 48 hours prior,you woul have to make arrangements with them on how to handle it.
The cost is $45.99/adult per night and $11.99/child per night.