You'd need to hack the journal.php Look for /* View Journal Page */ and find:
PHP Code:
//check if user is owner of journel or user is admin.
if(($bbuserinfo[userid] == $userid) || ($bbuserinfo[usergroupid] == "6"))
and take out the
||($bbuserinfo[usergroupid]=="6"
If after doing that, the EDIT option still comes up next to the private entries, you'd hack the /* Edit Entry */ code in a similar way to prevent the admin from just clicking EDIT to read the post.
Of course, none of this is bulletproof; if you have database access you can read all you like.
Regards,
Matt