How to use multiple root-hints files to recursively resolve different zones?

[Danny Bautista via Unbound-users]

I have unbound set up to do recursive domain name resolution using the 
internic.net root-hints file, but I would also like to be able to 
recursively resolve OpenNIC domain names using the hints for OpenNIC. 
I'm using the config below, and whenever I try to lookup opennic.glue, 
it just tries the regular nameservers rather than the ones specified in 
the "glue" auth-zone root-hints file (and fails, of course). What am I 
doing wrong? Is auth-zone even the right approach?

server:
  interface: 127.0.0.1
  interface: ::1
  chroot: ""
  use-syslog: yes
  do-daemonize: no
  username: "unbound"
  directory: "/etc/unbound"
  tls-cert-bundle: /etc/ssl/certs/ca-certificates.crt
  root-hints: root.hints
  trust-anchor-file: trusted-key.key
  log-servfail: yes

auth-zone:
  name: "glue"
  #master: 75.127.96.89
  zonefile: "/etc/unbound/opennic.hints"
  for-downstream: no
  for-upstream:yes
  fallback-enabled: yes

remote-control:
    control-enable: yes
    control-interface: 127.0.0.1
    control-port: 8953
    server-key-file: "/etc/unbound/unbound_server.key"
    server-cert-file: "/etc/unbound/unbound_server.pem"
    control-key-file: "/etc/unbound/unbound_control.key"
    control-cert-file: "/etc/unbound/unbound_control.pem"