Circumvent the Harmony remote device limit with this hack (pictures)

Click the "Add a missing command" radio button and name the command. You'll want to use a name that corresponds to one of the remote buttons of the phantom device. To avoid confusion and repetition, and to group the new commands together, I suggest you preface this and all succeeding names with a unique designation, such as "a Roku" (the "a" floats it to the top of an alphabetical list). Hit the Next button.