You will have to create fenced networks manually on the ESX,and for this you will need to build a "router vm", so you will be able to isolate the network traffic. You can see the example on the VMware doc: http://pubs.vmware.com/vsphere-4-esxi-installable-vcenter/index.jsp?topic=/com.vmware.vsphere.esxi_server_config.doc_41/esx_server_config/security_for_esx_systems/c_example_creating_multiple_networks_within_a_single_esx_host.html
It may seem difficult but once you have the router VM done you can clone it easily.