I have done that lab in DCLOUD. this is a tricky as far as i remember that lab and doing some thing similar in real life/production network there is a high chance to make a minor mistake and minor mistake can cost you to travel to site.
Is the only option at this point to setup a NAT on the appliance to accomplish this and, if so, can I put a port in the host definition on the FMC so that I'm able to differentiate between the 2 devices that will have the same public ip address?
yes, that possible. let see what other says, with more experience in this.
please do not forget to rate.