I just did the seafoam treatment on my car at 32,XXX miles prior to a catch can install. I personally put half a can in the oil, drove around a day (this won't, or shouldn't cause smoke) then the following evening I put the rest of the can into my gas tank w/ about a 1/2 tank of gasoline. I continued to drive it for about an hour or so. Then went home, put another 1/2 of a can into my vacuum line while my buddy held the throttle at about 2,000 rpm. He gave the motor a few good revs, then I let the motor sit (off) for about 5 mins. I repeated the process again, let it sit for about 15 mins (off). After the 15 mins were up, I started the car again, let it idle some, gave it a few good revs (around 4,000 rpm), then held it at 2,000 rpm a few times. I then let it idle for another 15-20 mins. it smoked a pretty good bit after sitting, but it's normal and I could tell that the seafoam was burning off all the oil and carbon built up in the motor. The motor runs stronger for sure now. (or maybe it's just in my head....?)
I know you have a ZL1 and I have an n/a SS, but that's how I did it, and I looked into my intake before and after, and it is a world of difference. (I also changed the oil after this seafoam treatment and installed a catch can)