You'd have to break your stay into two separate reservations. And then you could only use the dining plan on the days that you have it connected to your reservation. So, if you only buy the plan for the first 7 nights of your stay and then book an extra 2 night reservation without the dining plan, you will not be able to use any leftover credits for those last two days - they will expire the evening (not sure of the exact hour they expire) following the last night they are connected with.