In what way does it not work for multi-layers?

Module::foo(
  blah => 'zap',
  baz => [ 4, 12, 15, 'Fibonacci' ],
  froop => {
    thwap => 'funny'
  },
);
[download]

should work just fine when coerced from @_ to %args. The only thing to watch out for is if the same sub can be used as an object method, then you'll want to check that first:

  my $self = undef;
  if (ref $_[0] and UNIVERSAL::isa($_[0], __PACKAGE__))
  {
    $self = shift;
  }
  my %args = @_;
[download]

(untested)

Now, granted, a hashref can be faster than this, but that wasn't your question.