Part of me thinks that Smith could start with Gay at the 3. Smith is still a good weakside shot blocker and a versatile defender who can cover 2-4. The problem is that his career usage rate is around 24% or about the same as Rudy Gay. Rondo's career usage is about 19%. Cousins is about 30%. That leaves a 5% usage for whoever is at shooting guard. If Smith can agree to a 10-15% usage rate on kickout corner threes (he shot 35% from corner and elbow threes with the Rockets) or easy finishes inside, he might fit in with the starting five.
Otherwise, he needs to be the sixth man to lead the bench unit. I can see a rebound and run second unit of Collison, Marco, Casspi, Smoove, WCS beating opponents up and down the floor. That unit has four guys who can push the ball in transition, four guys who can finish inside, and three and a half guys who can knock down corner and elbow three pointers on the secondary break.