His theory might work but its based on if the rings are carboned up and stuck. ATF is a pretty decent solvent and its loaded with detergents. Chemicals like B12 chemtool and seafoam might actually work better. If the blow by is due to worn cylinders or rings you probably wont help a thing other than cleaning the tops of the pistons.
If you have tranny fluid laying around then go ahead and try it since its a free. Get an oil squirt can or turkey baster or something to squirt the oil into the spark plug holes, do all of them. After letting it sit overnight be sure to crank the engine over for a few seconds before installing the spark plugs to blow the oil out and you might throw a couple rags over the holes to save a mess. Put the plugs back in and drive it around for awhile. If it seems like it worked then try it again. If you want to try a more aggressive cleaner, get the B12 or seafoam. You might consider an oil change after youre done because whatever chemical you poured in, some of it might have creeped into the crankcase, the little amount of ATF would be ok, but you might not want an unknown amount of B12 or seafoam in you crankcase/oil.