Hello,
Currently Cambium's ePMP family of products does not support this feature. Your ePMP SMs would need to be configured in NAT mode for the SMs to use their MAC address for all traffic out of the SM. On the other hand, Cambium's PMP family of products (e.i. PMP 450, PMP450i, PMP450m, etc) do support a "Translation Bridging" mode that does what you have described, and it is described here: http://community.cambiumnetworks.com/t5/PMP-Getting-Started/Network-Address-Translation-NAT/td-p/39288
At the moment, I do not believe we have plans to implement something like this in the ePMP family of products.
Regards