Not a real clean answer, but here's something:

my $q = CGI->new;

my $str = $q->table({-border=>'1', -cellpadding=>'2', -cellspacing=>'2
+'},
  $q->Tr({-align=>'LEFT', -valign=>'CENTER'}, [
        $q->td(['one', '1', 'I']),
        $q->td( {-junk=>'', -colspan=>'2'}, [ 'two', '2' ] ),
        $q->td({-colspan=>'2'}, ['three', 'III']),
        $q->td({-colspan=>'3'}, ['four']),
]));

$str =~ s/(?<=<td)[^>]*junk[^>]*//i;
$str =~ s/junk[^>\s]*//i;
[download]

Update: Ignore this, good answer below