my $obj = Class->new(...your args...);
my $subobj = Class::SubClass->clone_from_parent($obj);

package Class::SubClass;
...
sub clone_from_parent {
  my $class = shift;
  my $obj = shift;
  my %args;
  ...set up %args by calling methods on $obj to get info...
  return __PACKAGE__->new(\%args);
}