Also, you will need to book the cash portion through Member Services, possibly at the 25% member discount, or possibly not with a discount. That depends upon discount availability, which is not always available.
If you book through CRO for say, an AP discounted room, then they cannot be linked together. You can request to possibly be in the same room, but no guarantees. However, in that case you could then purchase the DDP for part of the stay, not all of it as mentioned above.