Smoking with chips after sous vide
A small shot of liquid smoke added to the bag before cooking the rack sous vide will give it a mild smokiness that captures most of the flavors of real outdoor cooking.

With a grill and wood chips you can still impart some flavor. Try to keep the temperature low (say 300°F) to avoid negating the effect of low and slow sous vide. To avoid drying it out, don't post-sous vide smoke it for more than 3 hours.

If you want the deepest smoke flavor you would want to smoke the meat from raw and could use the sous vide to finish it off (the flavorful compounds in smoke will adhere to and penetrate raw meat much better than they will cooked meat).