We didn't extend our trip, but I did win a trip for a family of 4 and we have 5 people. We asked and they said we would have to arrange separately for the 5th member. So my husband became the default 5th member, as the kids had to be under the care of an adult and I was the technical winner of the trip. Essentially, we coordinated the 4 winners package, and then once confirmed my husband booked his stuff separately, which was a flight and theme park tickets. I suspect you could do the same, just tell the place that you have won x number of days, and would like to pay separately for x additional.