DB<114> sub doc { return }
 => 0
 
  DB<115> sub tst { 
           doc q/blab bla bla/; 
           return "tst" 
          }
 => 0
 
  DB<116> use B::Deparse
 => 0
 
  DB<117> print B::Deparse->new()->coderef2text(\&tst)
{
    doc('blab bla bla');
    return 'tst';
}
[download]

The book Perl Hacks showed another approach, I can't recall the details, IIRC something with attributes which assign a text to a hash with subnames as keys.