Well let's see if it is that clear:
Section 3.2: Appointment of Hearing Officers
8. If there is a vacancy on the Court, or any Justice is unavailable or has a conflict of interest the remaining Justices will promptly appoint a hearing officer to participate as temporary Justices.
9. If no Justices are available or all Justices have a conflict of interest, the Delegate will promptly appoint the needed hearing officers with the agreement of the Speaker.
10. In implementing the previous clause, any person who has a conflict of interest will be treated as absent.
11. Any hearing officer appointed under this Section must not have a conflict of interest and may not hold any other office while serving as a judicial hearing officer.
If in clause 9 'justice' refers to sitting justice and not a THO, which I think it does, then the delegate must appoint any additional officer. Thus, a THO could not appoint an additional THO even if there was a vacancy needing to be filled.
If my interpretation is different than the court's, I'd like the court to make a ruling on this.