Your buddying up idea is a good one. As you said, it's car/truck only, and you have to have a cabin. I'm sure there must be passengers traveling alone, either truck or car, who would gladly share the cost of the trip, with the proviso that they now have to share a cabin.
My guess is that if foot passengers were allowed, and booked a cabin, then there would be empty car spaces, which would be more lucrative than the occupied cabin space. If I remember correctly there are only 120 cabins.
How you would make contact is another matter. Possibly through the internet?