I have read that a member here was successful, once, and it wasn't recent. I will try to find it. It was mentioned in speckled hens thread about her double yolker.
Krista
I was waiting on an egg to hatch for 25 days. I seen movement at day 18 (my candleing skills are not that great). The egg DID NOT hatch. It was a double yolker. If I knew that I wouldn't have set it. Looks like 1 chick was was very developed. But the other did not develope I would guess past day 10. So from my limited personal experience I would say it's very difficult to do.