This trick is the same idea as an open box of baking soda in the fridge. I know that baking soda really isn't that expensive but I hate paying for it when there is a recycled alternative. Besides if you use baking soda to minimize odor you can't use it to cook because the same odors end up in your food. I also work in coffee so usually even that is free for me. My grinds that would just go to the compost pile get a new lease on life; though they do end up there eventually when it's time to refresh the deodorizer.
Take the used coffee grinds and spread them out as much as possible on a piece of foil. Let them dry completely (they will have a lighter color and be dry to the touch). This prevents them from growing excitingly bright colored mold. Also, if there is less moisture in the grounds they have more room to store all those odors you don't want. This drying can take a few days. If you live in a high humidity area, like I do, you can try to speed up the process. I set mine on top of my toaster oven each morning and watched them closely to minimize a fire hazard.
Decorate your plastic container to make it identifiable in your fridge so you don't throw it away. I did this mainly because I have three roomies and we all share the fridge. Also, I think it looks sweet.
Poke holes in the lid so the grinds can do their work. The more the merrier! I started with a paper clip, but safety pins are way easier. You can use an ice pick or even a hole puncher if the holes it makes are small. Don't use a big one though, or you may end up with grinds all over the place when you knock it over getting a midnight snack.
Fill it with your dried grounds and pop it in the fridge. You'll want to refresh the grinds every month or so.
**If your freezer is stanky too you can put dried grounds in a piece of pantyhose, tied off at both ends, and it does the trick nicely.