You can even try brass strip/foil, try a test length first, basically you can flatten the wire so that a thick wire carriers the as much current as the same wire smashed flat. This is true to a point, supper thin and you will have problems laying it down with out stressing/tearing the foil, and these stress points will have higher resistance than they should.
Just try the length and thickness on the bench before cutting into the model to be sure they work.
Also brass or nickel-plated photo etch is best since you can solder right to them, scrap brass from photo etch can be used, I have used copper tape, but you might not find this (we have it at work).
Here's some copper tape, power is connect at both ends, for redundancy:
http://www.kc6sye.com/images/images_05_ ... c_dckd.jpg
The connections were made by drilling a small hole through the end of each rail. The wire was stripped, very small wire, and soldered down was flat as I could manage, then a bit of brass from some photo etch leftovers, was tined on one side (small amount of solder) then that side was laid down on top of the wire end and heated with the soldering iron pining in place until the solder squeezed out. This protected and connected the wire end. Hiding the solder joint.
http://www.kc6sye.com/techmages_5_4_04_e.html