The trick is to convert "fly in amber'' into "fly fly amber'' (a harmless name) before the parser gets under way.

[ BeforeParsing i j;
  for (i=parse->1,j=2:j<i:j++)
  {   wn=j-1;
      if (NextWord()=='fly' && NextWord()=='in' && NextWord()=='amber')
          parse-->(j*2-1) = 'fly';
  }
];