Check these threads:
http://forum.mikrotik.com/t/port-to-interfacing/97096/1
http://forum.mikrotik.com/t/how-to-allow-two-devices-with-same-ip-access-internet/115990/1
But remember, it’s all wrong, ugly hacks. 
Check these threads:
http://forum.mikrotik.com/t/port-to-interfacing/97096/1
http://forum.mikrotik.com/t/how-to-allow-two-devices-with-same-ip-access-internet/115990/1
But remember, it’s all wrong, ugly hacks.