Hilton points are probably the easiest to generate given your time frame. Between the Virgin, Hawaiian (B of A & B of H) and various HHonors cards (Citi & Amex), you and your fiance can each generate 250k to 300k in sign-up bonuses easily. Sign up for the Amex card that gives you gold status within a year of your stay and you should get a discount on the points required for a room. You should have more than enough for a standard room at the Bora Bora/Moorea/Maldives properties (assuming availability, which could be an issue).

Once the standard reward room is booked, you can usually call the hotel and negotiate a cash upgrade to an OWB.