Somatic mutations for normal WES samples

I am trying to identify somatic mutations on healthy subjects (specifically in WES samples). As of now, I have found a couple of papers who have done similar studies such as this paper where somatic mutations in healthy subjects are identified (using RNA-SEQ data). But in my case, I want to find somatic mutations from normal WES samples. For somatic mutations, we need both tumors and matched normal samples to identify somatic mutations but how to identify somatic mutations from normal samples only. Please suggest. Thanks.