To turn off the ability to rate a member you can edit the showprofile.inc.php script. Line 174 you'll see this:
if ($config['USER_RATINGS'] == "1") {
Just change that to:
if (($config['USER_RATINGS'] == "1") && ($UNumber != '###')) {
Change, ### to the actual userid of the user in question.
To disable the display on the posts, it would probably be easiest to just clear out their current rating in the database.
UPDATE ubbt_USER_PROFILE set USER_RATING='0' where USER_ID='###'
Again, just change ### to the userid in question.