One strategy is for you to register users directly in the registry, giving them limited permissions. Not what you are looking for, BUT – this can get you what you want. When you register them in this way, they get run through the approval process, get accepted, and are given registration codes.
Then, you can have them register themselves at a later time using their email address and the Paratext 8 code you received. They will be approved immediately.
Not sure why you are registering for them, but often people want to be prepared for a workshop by having the codes all in advance. This will get you there because on Day 1 of the workshop, everyone can activate the codes you have already received and have full privileges.