What do you mean starting from scratch?
If connecting the new drive and copying the contents of the old drive to the new one is too much work, I'm not sure what to tell you. There is no way to get data from one drive to another without doing SOMETHING to make that happen.
I'm totally not understanding what you mean by "starting from scratch" because it couldn't actually be any simpler than copying everything from one drive to the other and then either telling your game launcher where the files are at now when you fire them up for the first time, or else changing the drive letter of the new drive to the same drive letter that the old drive was so there is no need to modify the game launcher configuration at all. I don't know how the process could be any easier than that?
You said the OS wasn't involved since that is on a different drive, so this should not be a complicated process, at all.