[Edited by vradeenian, 3/21/2014 7:44:18 AM]
Try the trainer first. As the GOG version should not be anything different.
I did. couldn't even activate. And its different, Coz GOG version is 1.6. Not 1.55 like steam.
Next time wait to see if a trainer will be made for the platform you are looking to buy it from. Before buying. Since it was done for steam ya should have went with steam.