I would put scent in my plastic during it's last microwave introduction, and then again when I bag them....complete overkill I have come to learn. Like Jason said, when you add scent to the bag, the baits soke them up like a sponge over the course of a few days. So, I will not be adding scent,or at least AS MUCH scent during the cooking process anymore.
And a side note, I literally just got done reading an article that spoke about scents. It was in bass angler magazine, September 2011 issue, just came out. It spoke about the whole topic of scents, etc. Something that I did not know is this;
"bass use their sense of smell to detect prey, find a mate, and detect pollutants. They can smell the presence of pheromones, sugar, salt, alcohol, amino acids, and bitter substances. Because bass can only detect biological or chemical scents that are water soluble and in molecular form, any attractant or stimulant that is oil based will not be perceived since oil is insoluble in water and the attractant molecules too large. The chemoreceptor can only detect scent molecules that are the same size or smaller than the receptor itself."
It does go on to say however the oil based scents will mask other odors....
So, what I take from this, oil based scents will NOT attract fish, but will mask deterrent odors.
There's a lot more in the article, very good read!