Well, add conditions to all the events where nicks are added (on join, on nick, end of who, ...)
Code:
; at the nick event
    if (ustreamer-* !iswm $newnick) { -nick adding- }
; at the join event
    if (ustreamer-* !iswm $nick) { -nick adding- }
; etc

Maybe you're lucky and your script uses a distinct routine (alias) for this - so you have to put the extra condition only at one place.