You want your official (pkg) games (stored on internal drive) to transfer to your external harddrive so you can play them from your external drive?
That's not possible I suppose. They don't become fpkg games when moving... Maybe, just maybe they do transfer, but you probably need to change the games so they become fpkg.
I did notice app2usb created maps for my official games on the ext. hdd. Do you see the maps of those bought games on your ext. hdd?