I'd like to propose an alternative solution: passenger missions stay as they are, but we also get a "passenger market" where we can "buy" passengers (or more accurately, sell tickets).
Basically, instead of doing what we do now, which is actually very odd (right now we say "I've got this giant space ship, please someone charter me") instead of that, we do what happens in real life, we say, "I'm going to system-X, and I have Y tickets for sale."
The point of all this is, the purpose of a Beluga is that people would actually pay to travel in one, just like people will pay to travel in an Airbus A380. So if you have a Beluga, and it's parked at a planet, you should have no trouble selling tickets to whatever destination you name. By contrast, while it's true that an Anaconda can technically carry more people, that's like saying that a military aircraft can pack more people into it than an A380 - technically true, but you would buy a ticket to fly like that.