I had proposed a nexus mechanism in the City Hub topic, and I'll reproduce it here:
on a wall of the nexus/hub are three clickable buttons, each below a window that displays a number. The numbers 0-9 are textured onto a 10-sided shape, of which only one side is visible through the window. Each time the person clicks the button, the shape rotates to display a different number. The person clicks the buttons until the desired shell number is displayed.
When the player has finished dialing up the shell number, they press the fourth button. They hear the whirring of massive machinery all around them; when the sound stops, a door slides open, and inside a hidden alcove is a pedestal containing the linking book to the shell. Sort of like the Nexus, except on a larger scale: imagine a ring of pedestals circling the map room just beyond its wall. Only one pedestal/book is visible at a time.
[Art/Programming spoiler: actually, there will just be one pedestal/book. You'll just be led to believe there are 440 pedestals out there...]
I initially tried the clickables approach to this, but did not have much success. So, now I'm trying Dustin's "proximity click" approach. I'll tell you the results, once I get a chance to experiment further.
Tweek: I'm very curious - what is your idea?