wouldn't any co2 you put into the tent get sucked up in the inline anyway? the only way I can see the technique working is if you let your plants stew in the co2 with the fan off for an hour or more?
50 grams baking soda, 50 grams citric acid, punch few holes in a bag, hang it around 30cm above canopy. That's 1 bag per 1 plant.
I've seen good results on another forum, try it out. It's cheap and simple so why not.