So where does all this leave poor dear Bilbo? Surely not paired with no one but that nasssty Sssmeagol ...
I suppose that he might be paired with Frodo, since they both share the same fate. But Bilbo's adventure could hardly described as spiritual (save in the sense of "unearthing" the Ring). Yet he ends up with the "calling to a higher place" scenario instead of the happily married with 2.4 kids one.
As for pairings within the Fellowship, we have Frodo/Sam, Merry/Pippin, Legolas/Gimli and (conceivably) Aragorn/Gandalf, leaving Boromir as the outsider. Which, I suppose, is appropriate since, out of them all, he was the one least comfortable with their mission.