Why would you use Gatwick (or any of the London airports for that matter) for your crew change point? There are heaps of airports in the UK with either an air or nearby rail connection to an international airport. Use one of those instead. Of course you have to get there too but even so...
Wick is used to dealing with ferry flights and has air links. Sumburgh & Kirkwall have air links to the mainland if you want to have a jolly in Shetland &/or Orkney, respectively, on the way.