Cod isn't a very oily fish, so I'd sit it on oiled foil. Even if it sticks a bit, you can flip it over and peel the foil off. Failing that, put it on a metal tray. You'll still get a smoke on the three sides that aren't touching metal. Or skewer it, and be ultra gentle with it once it's cooked. Or skewer it and give it a sticky glaze so it holds together.....
I didn't smoke it at all, it wad just a quick test. I had 30mins to prep, eat and tidy up after! Had people viewing house. Mrs got it in her head she wants to move.