Somewhat off the top of my head ...

package My::App;

# ...

require Config::IniHash;
sub _configuration
{
  my $self = shift;
  unless ($self->{_configuration})
  {
    require Config::Find;
    $self->{_config_name} = Config::Find->find(name => 'myapp',
                                               mode => 'read');

    if ($self->{_config_name} and -e $self->{_config_name})
    {
      $self->{_configuration} = $self->_default_configuration();
    }
    else
    {
      $self->{_configuration} = Config::IniHash->new($self->{_config_n
+ame});
    }
  }
  $self->{_configuration};
}

sub _default_configuration
{
  my $self = shift;
  unless ($self->{_default_configuration})
  {
    # Config::IniHash docs don't say that it can take
    # a glob, but the code does.
    $self->{_default_configuration} =
      Config::IniHash->new(\*DATA);
  }
  $self->{_default_configuration};
}

__DATA__
# defaults go here.
[section1]
key1=default value 1
key2=default value 2

[section2]
key1=default value 2-1
[download]

Because of the way that IniHash works, you may have to do something like this to use it:

my $value = $self->_configuration()->{section1}->{key1} ||
  $self->_default_configuration()->{section1}->{key1};
[download]

Off the top of my head, I can't think how to combine them. Good luck!

PS - looking at the code I have this in, I'm using Config::Natural, so I have a sub that is "get_config", and I pass in the config var I want, and it does the work of checking the config file vs the DATA (defaults).