Run them underneath from behind and use wire seperators. By using 8.5 wires the combonation of "stiffness" and seperators will hold them in place under the tubes. It also depends on what type of header you use. The orange car had full tube headers and the green car had block huggers. It is nearly impossible to do with the block huggers because of the tube configuration.
Note the difference here:
Tucked under and hidden:
Run down the side of the valve cover but on top of the headers:
