i've not heard of the tide stain pen bleaching out fabric dye but the clorox bleach pen will. just draw on the design let it set a few minutes and wash as usual. don't let it set too long or it will spread out as the fabric absorbs the bleach. it may take two or three washings to finish a project depending on how detailed it is.
Martha Stewart did this on her show with stencils on t-shirts, so I'm sure you can adapt it for denim. One thing that was apparently important was to neutralize the bleach so that it would not eat on the fabric. Anyway, here's the link to the page where she did the t-shirts.
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