You don't need Garmin's Communicator plug-in.

Create the route on mapping software that can save as a TCX.

When completed, connect the Garmin to your PC and treat it as a "Mass Storage Device" (i.e., like a hard drive)

Locate the Folder "NewFiles".

Drag and drop the TCX file into the "NewFiles" folder. (Multiple files can be done at one time)

Disconnect the Garmin from your PC. (Best to use the tray icon to 'Safely Remove Hardware')

Once disconnected, turn the Garmin device on. It will start converting the files from "NewFiles" into FIT course files.

Once the conversion is complete they should appear under COURSES on your device (and the FIT files should appear in the "Courses" folder on your device)