Manston should investigate the promotion of fly/cruise packages.
This is one area in which they definately have the capability to accomodate the largest aircraft and the catchment area to make it commercially viable.
I would suggest that it costs operators a fortune to put such charters on from Gatwick, and a reputable agent, such as Newmarket Travel etc. have the contacts to advise accordingly.
Even if it's only 5 or 6 flights a year, that's 3000 to 4000 passengers using the airport which weren't there before.