I actually think you can't or maybe this may vary by location. In AZ I was told by a "Master Electrician" <-- Joke, that I couldn't do that and I had to run conduit all the way to the sub panel and then just continued the THHN all the way through. It's of course safe to do that and in that application was convenient and very simple so I didn't complain.
10/11: Bought the perfect house;
11/12: 10k & 200 hours,08/13: 30k & 400 hours into the perfect house, 12/13: 35k & 500 hours
02/14: 37k & 550 hours, 08/14: 38k & 650 hours
05/15: 40k & 700 hours and I think it's done, Home appraised +40k!!! 1 to 1 ratio achieved!