It's the other way around, you take something from your dream and associate it with the peg. So if you were dreaming of, say, chickens, you visualise a chicken doing something with your peg; like let's say your peg for the number 1 is a tree, you can visualise a giant chicken sitting on top of the tree.

When you get up in the morning, you recall the tree and see the chicken on top of it, the chicken reminds you of the dream you had about chickens. It may or may not be enough to recall the rest of the dream.

I still use a dream journal and when I can't be bothered getting up, I record myself talking about the dream on my phone and write that down later.