I've had several people ask me about these, but alas, they don't work with us average travel agents, so it's not something we get involved with. But I do know of a couple of websites a friend of mine turned me onto;
Maris Freighter Cruise and Travel Club -- Around the World Cargo Cruises
And the other one; Freighter Cruises
Perhaps those will be of help to him.
45 Cruises & Counting! Favorites: Paul Gauguin to Tahiti: Uniworld River Cruises in Europe; any of the Celebrity Solstice-class ships; Holland America for 12-nights in the Baltics & Russia; RCCL for 14-night Greek Isles, Turkey, & Croatia; Holland America for 14-day Alaska cruisetour; 10-night Canada/New England cruise; 21 days in Hawaii including a 7-night NCL cruise; Oceania for 25 days in Asia; & 3 months touring Europe by train. And many days spent in all-inclusive resorts!