Oh well... here is how I think he did it.
I think he gave a few clues away. The first was when he said he may get 5 of the numbers, the second was when he said it took a year of his life.
Firstly, I believe the BBC footage was superimposed onto the TV set, almost certainly from the point where the draw ended. I believe that many possible takes were filmed and the correct one played at the last possible moment after the bonus ball was selected. Derren's 'correct take' starts from the end of the numbers being drawn and of him writing out and reading the numbers before displaying the balls was chosen . Yes the BBC footage was live, but the sequence where Derren writes down the numbers I believe was pre-recorded and was one of many several thousand takes filmed over the year. I calculated that it would take years of consecutive filming to produce all 14 million outcomes, but he may be able to film enough to get his 5 numbers, and 6 if he got a lucky guess - which he did!
The camera slightly moves as the numbers come out, Derren keeps still and has his hand over his mouth, I believe there is a point at which the film changes to the correct selected 'take'. As each ball is drawn this rapidly shortens the list of takes to choose from.
Well done on Channel 4 for a smooth transition on the changeover point!
I will have to wait for Friday before I find out if I am right. What do you think?
For those of you that don't read comments I am adding this!:
He wouldn't need to film 14,000,000 takes, just 1,000,000 in order to cover geting 5 balls correct. He then has a 1 in 14ish chance of getting the 6th ball right - which he did! Either way it is a lot of filming for a year!!
Another theory could be that there is a split screen, where the left hand portion of the screen appears to be live, but it is actually frozen. Some one can walk on without being seen and place the correct numbers there, and then the left hand section of the screen can be 'un-paused' when Derren walks over.