Is this what you want ?

                     {
                       'class' => 'myclass',
                       'set' => {
                                'key2' => 'b',
                                'key1' => 'a'
                              }
                     }
[download]

XML::Rules is simpler than XML::Simple, you start with xml2XMLRules, and you tweak it a little

#!/usr/bin/perl --
#~ 2012-05-02-20:44:05 by Anonymous Monk
#~ perltidy -csc -otr -opr -ce -nibc -i=4     
use strict; use warnings;
use XML::Rules;
use Data::Dump qw/ dd /;

Main( @ARGV );
exit( 0 );

sub Main {
    my $t = XML::Rules->new(
        qw/ stripspaces 8 /,
        rules => [
            'obj'   => 'as array no content',
            'stuff' => 'no content',
            
#~             'set'   => 'as array', # original from xml2XMLRules
            'set' => sub {
                
#~ $rule->( $tag_name, \%attrs, \@context, \@parent_data, $parser)
#~ my ($tagname, $attrHash, $contexArray, $parentDataArray, $parser) =
+ @_;
                '%set', { $_[1]->{name} => $_[1]->{_content} };
            },
        ],
    );

    my $res = $t->parse( MyXml() );
    dd $res;
} ## end sub Main

sub MyXml {
    q{<stuff name="me">
    <obj class="myclass">
        <set name="key1">a</set>
        <set name="key2"></set>
    </obj>
    <obj class="myclass">
        <set name="key1">a</set>
        <set name="key2">b</set>
    </obj>
</stuff>
};
} ## end sub MyXml
__END__
{
  stuff => {
    name => "me",
    obj  => [
              { class => "myclass", set => { key1 => "a", key2 => unde
+f } },
              { class => "myclass", set => { key1 => "a", key2 => "b" 
+} },
            ],
  },
}
[download]