I’m gonna continue discussing this feature, but for the record, wouldn’t mind at all if you left this out for later.
Perhaps the easiest way around this would be an alternative invite feature, more akin to that of Google Groups when you “add user directly”. A simple interface to allow admins to bulk-add users to the forum, as well as to any groups of their choice.
Many mailing lists and newsletters have this feature (I’ve found Mailchimp to be an excellent example with its duplicates checks and smart format reader) and I don’t see why it shouldn’t be part of a forum as well. As long as you have users’ permission (as you are required to by law), it is a highly effective way to kickstart your new community.