You cannot, retention tags cannot be targeted to messages from specific senders only. What you can do is remove the default archive tag and use personal tags instead, which the end user can apply to messages as needed. Though judging by your description above, he will likely see this as overkill.
And alternative/mixed approach would be to use folder-specific tags instead, and combine them with Outlook rules. For example, you can have the content of the Inbox folder auto-archived, whereas items from said senders are moved to a different folder, say "important mail", are not automatically processed. Or do it vice versa, leave the content of the Inbox folder as is but only process items in other folders. The downside is that user-created folders will need to be stamped with personal tags, so again some sort of effort is required on the VIP's side.