I believe that in recent/latest versions of ROS, the 4 address support/station bridge mode has been implemented:
http://forum.mikrotik.com/t/using-wifiwave2-to-bridge-two-audience-wirelessly-thoughts-4-address-mode/153357/1
but I have not seen complete/reproducible examples on its use.
In any case, probably CapsMan - even if it would work, which is not given - seems to me a complication for just two devices.