Question about using Object in Nomad-pack

Can anyone tell me how to pass an object on the command line with --var to nomad-pack? In the hello-world example, in _helpers.tpl, there is a section for a service and I would like to use at least the upstreams portion

              [[- if gt (len $service.upstreams) 0 ]]
              [[- range $upstream := $service.upstreams ]]
              upstreams {
                destination_name = [[ $ | quote ]]
                local_bind_port  = [[ $upstream.port ]]
              [[- end ]]
              [[- end ]]

I can not work out the correct --var to use to pass the object so it loops across a number of upstreams.

Any help would be appreciated.