Hi,
You can configure multiple IP Interface on the ESA appliance to route the traffic through a different Data port on the ESA appliance.
On the data port, make sure to disable the spam quarantine access on the Management interface and enable on the data port:
* Spam Quarantine HTTP
* Spam Quarantine HTTPS
Instruction guide to do this is available here:
http://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/118692-configure-esa-00.html