Try this:
Create a shortcut on your desktop that points to your new hard drive.
Double click it to verify that it works.
Open your My Tivo Recordings folder and drag and drop the shortcut into it.
The next time you access your computer from the Tivo, you should see the hard drive in the list. In your case it should appear as Tivo (J: ).
I have done this with 4 different drives.
Create a shortcut on your desktop that points to your new hard drive.
Double click it to verify that it works.
Open your My Tivo Recordings folder and drag and drop the shortcut into it.
The next time you access your computer from the Tivo, you should see the hard drive in the list. In your case it should appear as Tivo (J: ).
I have done this with 4 different drives.