https://vborg.vbsupport.ru/showthread.php?t=183183
I use this, but usually the person has to post in the thread first...
Maybe if you get creative you could get it to work
--------------- Added [DATE]1238183686[/DATE] at [TIME]1238183686[/TIME] ---------------
Also, you can make a new, temporary board.
Admin CP -> Forums -> Forum Permissions -> Disable guests from viewing
Admin CP -> Users - > Search user -> Find the user you want to not see the board -> Edit forum permissions (access masks) -> disable that board
He/she will never see the board, or anything in it.