Unless you have a very strong addiction (sucking down a pack a day or more), it's easier to hide than you think, as long as you take a few precautions. Only smoke outside, preferably upwind; wash your hands immediately after smoking; use strong breath mints; etc. Also, if you work in an place where lots of people smoke (and you'd be amazed at how high the percentage of smokers is in a hospital environment), the "I just hang around with smokers" excuse goes a long way. I quit smoking years ago, and remain amazed how easily that smell attaches to your clothes if you do nothing more than hang out in a smoky bar for a half hour.
Anyone know just what Hacking's job was? If he wore scrubs, he probably changed them often, making it even easier to hide the smell.
Also, he may well have showered at the hospital everyday.
Why is that?