Don't know if you can rent out the partial reservation that you will not be using, but this is what we did when were presented a similar situation in which we didn't our whole reserved time.
We used the first four days of our seven day reservation. Then our friends flew in to take the balance of the seven day reservation. They did not go to the check-in desk to register but to pick up the envelope of keys and other resort related information that permitted them to use the balance.
When they checked out, anything and everything that they used that cost money was charged to my credit card. A few phone calls was what was charged.
Now, in your situation you are talking about renting out the rest of the days you don't use to perfect strangers. I'm sure there is a way to insure that you don't get whacked for the renter's costs incurred after you have vacated the resort, but it will probably be very messy; when you leave you take the renter and have the renter use his credit card for expenses he incur and the resort settles up with your portion of the expenses.
