So, from your default.conf file, you can do:

  ACCEPTABLE_LICENSES="foo bar ..."
  MKCONF_VARS="ACCEPTABLE_LICENSES"

  Rebuild your sandbox and you'll see ACCEPTABLE_LICENSES in the mk.conf file
  inside it.

I have in /etc/mk.conf

 .include /etc/mk.conf.include

and have a chroot-setup script that copies that file to the chroot, andb
puts the include line in mk.conf.  So then I have all my settings
propagated to the chroot.

-- 
        Greg Troxel <gdt@ir.bbn.com>