The solution is 2 parts hydrogen peroxide, 1 part Dawn dish soap (just the regular kind), and some baking soda. I also used a small scrub brush to scrub them really well. I did the cleaning in the bathtub since I don't have a laundry room. I scrubbed each dingy section for 1-2 minutes with the brush, then let the shirts sit for an hour before washing them in a regular wash cycle.
My before and after pictures aren't very telling. The lighting in my apartment isn't the best, but they were really truly dingy - like the picture above from the other blog. Once I started scrubbing I even noticed that some of the camis had blue on the bottom from where they had been tucked into my new jeans.
And a tip if you're going to try it - wear rubber gloves! My fingers are white. haha.
Worth it? Yes! The camis were a lot harder to clean because of the built in shelf bra layer and the tiny straps. The shirts aren't brand new white, but they're clean now rather than dingy in one area. I cleaned 15 shirts with this method and each one looks great.