Since I have some time to kill, here is what I would do:
Have one of your co-travellers sign up for a Gold after 4 stays promo (I assume you will have at least one co-traveller coming to both trips).
For the first trip book one room under his name for the 1st, 3rd, 5th and 7th night, so he completes the challenge and makes Gold. Book all the rest under your name to max points.
Book 2 rooms under your name and 2 rooms under your friends name for the second trip.
