As far as I know that's not possible to let vCD configure 2 IP addresses to 1 NIC. If you would configure the IP Mode of the NIC to DHCP or None does a reconfigure still changes the IP assignment? And yes, you need to configure IP addresses outside of the DHCP server and Static IP Scope.
I actually do this all the time with linux and nested ESXi on vcloud. You have to go into vcenter and find the vds associated with your org network and allow promiscuous mode and forged transmits. If you ever power the vapp off and back on, you will need to set these again as they are lost when vcd deletes and rebuilds it during power cycles.