This is by no means an easy or standardized task. Shaping GNR is at the forefront of science. One way is to buy nanotubes at a defined chirality and unzip them. How you place them where you want after that I have no idea. The conference proceeding I posted above had at least one talk about doing it, to my knowledge not yet published.
You should just invent your own method and publish it, at this point that would be some high impact work in the field.