Most effective method would be to extend the Map Modder to help do so automatically.
Have them use a mapping of 'current map' to 'next map', don't bother scanning for opposite direction portals (this means creating 'duplicate' portals, one for each direction)
Modified MapModder to help manipulate portals. Finished most entrance/exit style portals, but still need to find out where the one way after-boss portals drop you
Most effective method would be to extend the Map Modder to help do so automatically. Have them use a mapping of 'current map' to 'next map', don't bother scanning for opposite direction portals (this means creating 'duplicate' portals, one for each direction)