Although the enema idea is bizarre. I guess I've never been near addicted enough to anything to require that kind of drastic measure.
Rectal mucosa absorbs medication very well. In an emergency valium can be crushed or liquefied and put in the rectum for someone having prolonged seizures. Opiates for years have been taken that way, faster absorption than oral and almost as fast as snorting. It is called 'plugging'.