Not sure but in editpost.php(3) you need to change following lines.
if ($showeditedby==1 and $postinfo[dateline]<(time()-($noeditedbytime*60))) {
if ($getperms[canadminedit]==0 or $showeditedbyadmin==1 or ($getperms[canadminedit]==1 and $getperms[cancontrolpanel]==0)) {
$getorig=$DB_site->query_first("SELECT pagetext FROM post WHERE postid=$postid");
I don't have enough PHP skills to do this.