sub find_ids {

##</code><code>##

*find_ids = sub {

##</code><code>##

...
my ($class, $alias_for) = @_;

my $sub = eval "package $class;" . <<'__EOI__';
   *find_ids = sub {
      my ($class, $params) = @_;
      do_something_with($alias_for);
      return $class->SUPER::find_ids($params);
   }
__EOI__
die $@ if $@;
...