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.
Travel Agent/Cruise Specialist w/13 yrs exp and 48 Cruises on 11 cruise lines! Favorites: Paul Gauguin - Tahiti: Uniworld River Cruises - Europe; Celebrity Solstice-class ships; Holland America - 12-nights Baltics & Russia; RCCL - 14-nights Greek Isles, Turkey, & Croatia; Holland America - 14-day Alaskan cruisetour; 10-night Canada/New England cruise; 21 days Hawaii w/7-night NCL cruise; Oceania - 25 days in Asia; more than 3 months touring Europe by train. And many all-inclusive resorts!