Bukkit

Make this an optional feature
Something like scrollingPortalSelection: true

Feature:
Right click the sign on the portal to scroll through portals on the chain.

Use recursion for this feature to cycle select to the next one
Get name of portal warping to by last line of sign
Then recursively call portal.getLinkedPortal() and compare name with the last line of sign.
Once you find it, set the last line of the sign to the found portal's linkedPortal.

If this feature is requested enough, I may add it.