Why not just have a roller, a la vintage Salsa stems?
I worked on plenty of bikes with stems like this back in the late 80's early 90's that routed the brake cable through the stem one way or another. The annoying problem with this on a quill stem is that anytime you move the stem you have the additional job of re-adjusting the brakes as well. Not sure this is a huge jump forward technologically, but hey, different strokes for different folks I suppose...
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