I assume that you have disc brake mounting bosses on the frame, otherwise the project is DOA.
There are metal clips made to hold cables, but the tube diameter selection is limited. Or you might try to locate some of the glue on guides used for carbon frames, but I wouldn't bother. Turns out that not only are cable ties the easiest solution, but they work as well or better than most of the other options.
What's your objection to using cable ties?
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