Go to Content Manager. Find the train.
Right-click on it and select Show Dependencies. On the window that opens up, select "View in Main List".
Find the bogeys in the main Content Manager window. Right-click on one and go to Edit, then select Open In Explorer. This will bring up the asset in an explorer window.
Go to the "config.txt" file. Find the direct-drive tag and set it. If it isn't there, then add it in the first block of text.
Save the .txt file exactly where you found it, and under the same name, overwriting at the prompt.
Go to Content Manager and go Edit > Commit.
That's it.