I've done it. Get a London Broil (which is usually a top sirloin). I usually have the meat deparment slice is as thin as they can (1/8th of an inch). Marinate overnight in soy/L&P/hot sauce (to taste)/garlic powder/cayenne (careful)/ and lots of cracked black pepper.
Soak your wood of choice overnight (fruit woods are good).
I used a bullet smoker. hang the meat over the grill, and smoke over very low heat for about 8 hours. once a small charcoal fire is going, throw some wood on. Usually you will want to add a coal or two every 15-20 minutes - I usually keep a second charcoal fire going to have lit coals available. Add wood as needed. You should be smoking at around 200-250 degrees.
Taste to determine doneness.