Is there a reason you want a flydrive? why not book flights and a car you want, when you want.
If you really want a flydrive then don't collect their car, book your own car, just don't tell them or they charge you an unpackaging fee.
Unless you have found a great deal on flydrive? I find them way OTT. Just compared our dates for next year, VH flydrive £ 2,815.49 + £324.35 int suv Total £3,139.84.
Flight only £1,875 on same flights + £279.45 same car Total £2,154.45