sub alpha; # unchanged from your example.
sub beta {
  my $self = shift;
  my $coderef = sub { $_ eq $gamma };
  $self->_internal_sub($coderef);
}

sub _internal_sub {
  my $self = shift;
  my $coderef = shift;
  foreach ...
    if ...
      if ...
        if ...
          local $_ = $baz;
          push @foo, [ @bar ] if $coderef->();
        }
      }
    } else {
      local $_ = $baz;
      push @foo, [ @bar ] if $coderef->();
    }
  }
  local $_ = $baz;
  push @foo, [ @bar ] if $coderef->();
  \@foo;
}

##</code><code>##

sub beta {
  my $self = shift;
  my $coderef = sub { $_[0] eq $gamma };
  $self->_internal_sub($coderef);
}

# and ...
  push @foo, [ @bar ] if $coderef->($baz);