I don't use BOC so I can't confirm, but according to FAQ, Kevin's response:
...
open BOClean's excluder and drag the icon for it to the excluder box (if you're not using Vista, you can drag a shortcut) and once it appears in there, close the excluder, close BOClean and restart it so it will pick up the fact that you want MIRC ignored and BOClean will leave you alone. Should *another* copy show up somewhere that you don't know about it, BOClean will let you know.
(I bolded instructions)