SRC MAC address masking for on-bridge service communications

Greetings;

I'm trying to setup a completely transparent brouting firewall/bridge.
Since I'm proxying a protocol with a userspace server, I've had to setup
 a BRouting firewall/bridge.  Much akin to a brouted squid proxy setup.

My problem is that the Machine currently exposes it's MAC address as the
SRC MAC for any communication that flows through the userspace proxy service.

 192.168.2.0/24
Internal Network
|
|
|  _____________________________________
| | Bridge/Firewall Machine            |
| |          ____ Proxy   ____         |
| |          |    Service    |         |
| |  ________|               |_______  |
| |  |                              |  |
| |  |                              |  |
| | /                                \ |
|_|/_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ \|__
 A |____________________________________|B |
                                          |
                               ___________|
                               |
                          10.0.0.0/24
                         External Network

Is there a way to setup the system up such that all traffic to/from
the machine has no MAC addresses associated with the machine?
ie The bridges MACs remain hidden ?

Any insight or suggestions appreciated;

Kane

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