Well, everything is possible with a source filter :) (Sorry, only solution I could think of.)

package DynPackage;
use Filter::Simple;
use Text::Balanced qw/ extract_bracketed /;

FILTER_ONLY
  code => sub {
    1 while s/\bdyn_package \s+ ([^\n]+?) \s+ (\{.+)$
             / do { my ($pkgcode, $stuff) = ($1,$2);
                    my ($code, $rest) = extract_bracketed($stuff,'{}')
+;
                    qq|
{ \$DynPackage::pkg = $pkgcode;
  eval "package \$DynPackage::pkg;" . <<'  DYNPACKAGE_AUTOBLOCK';
    $code
  DYNPACKAGE_AUTOBLOCK
}
$rest
|;
                  }
             /xes
  },
  # FOR DEBUGGING:
  # all   => sub { print }
;

1;
[download]

Later on...

use DynPackage;

foreach my $block ($self->get_blocks) {
  dyn_package $block->package {
    $block->setup->();
    $block->code->();
    $block->teardown->();
  };
  $self->_croak($@) if $@;
}
[download]