I doubt clay will have any effect on smoke on the inside of a windshield. You just need to do repeated cleanings of the area. I would give Stoner's Invisible Glass a shot. It works quite well and can be found at AZone, etc. A small waffle weave microfiber towel should give you good absorption and cleaning power.

 

One option that works really well is a mixture of vinegar and water 50/50. Using a good MF towel to wipe the windows down and a nice all cotton towel to polish it making sure to get any streaks out at the same time. Never fails to clean anything really. I use Stoner's glass cleaner too, but on the tuff jobs I pull out the mixture and I am never disappointed.