EcoRenovator - Electrical outlet infiltration gaskets

Hi,
We had an energy audit from our utility that turned out to be sort of a mixed bag, but they did do a blower door test which was quite helpful.

I had always thought that the leakage through electrical outlets was minor compared to other leak sources, but they felt that there are so many outlets that its significant, and you could certainly feel air inflow when the blower door fan was running.

They left some outlet gasket material that you can use to stop the infiltration -- its about 1/8 inch thick and made from foam -- you take the outlet cover plate off, place the gasket around the outlet and put the cover back.

I did a couple outlet with this and its easy, but I find that you still get air infiltration right through the part of the outlet that you plug the appliance into.

Just wondering if anyone knows a better way to do this? A better product or technique for stopping infiltrator through outlets?
Wondering about a little squirt of Great Stuff right at the back of the outlet box where the wire comes into the box?

Gary