You need one L3 interface per device with same IP address. It can either be a router with multiple routed ports or a VLAN-enabled switch with each pirt set as access port to different VLAN and backed with router using many VLANs.
There were a few discussions about the same issue before (solutions were fit for slightly older ROS versiobs, but should conceptually work with v7 as well):
http://forum.mikrotik.com/t/connecting-to-multiple-devices-with-same-ip-address/159052/1
http://forum.mikrotik.com/t/how-to-allow-two-devices-with-same-ip-access-internet/115990/1