You might want to take a look at how Pod::Usage does it. The following is a bit of a hack in that it doesn't use the module for its real purpose, but perhaps it's close to what you're looking for?

use warnings;
use strict;
use Pod::Usage;

=head1 SYNOPSIS

Synopsis

=head1 FOO

Foo!

=head1 BAR

Bar!

=head1 QUZ

Quz!

=cut

open my $fh, '>', \my $str or die $!;
pod2usage(-exitval=>'NOEXIT',-verbose=>99,-output=>$fh,
    -sections=>['FOO','QUZ']);
close $fh;
print "<<$str>>\n";

__END__

<<foo:
    Foo!

quz:
    Quz!

>>
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