Well, you could make an "in between" cell that just has 2 invisible autoload doors (like the ones you use on caves with no physical door) and have the exit from each door come out in the autoenter area of the other door.
If I have to, I'll try this. I just shouldn't need a hack to link two doors, regardless of where they are, right?
All the cities have their own worldspace, so, you could use city doors as an example.
I looked at the door into and out of WhiteRun, which teleports to a door in Tamriel, but it doesn't seem to have any different characteristics from other worldspace-to-interior doors.