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That's what I've done in the past.

They typically only need delegation for the first week or so, and many times I don't get their usernames from them until after they submit their first assignment.

This semester, after students claimed their accounts via HiveOnboard, I noticed that their RCs were showing enough for 7 posts (via hiveblocks.com), so I took that to mean they were all good to go for the first week. Apparently that was an incorrect assumption.