I am struggling to understand the actual difference.
Some people have two (or more) machines with the same IP that need to be reached remapping them to other different IP’s (usually based on which port they are connected to).
You have two (or more) machines with different IP’s that need to be reached remapping them to other diffeerent IP’s.
Isn’t your case a subset of the former?
If this is the case, maybe you might find of interest this thread:
http://forum.mikrotik.com/t/port-based-routing-to-2-identical-ip/180504/1