How can I do this in vBulletin?

[JamesC70]

Soft-delete the posts in question, and add a note as to why.

Then remind your moderators to search the members' post history when they soft-delete violating posts, and once a member reaches xx number of violating posts, the moderator should bring it to your attention for further review, suspension, or banning.

(Once your moderators go through this a few times, the infraction system and user notes will look easy in comparison. )