Just to address the comments raised by Mr. Dubé and Monsieur Paul-Hus in terms of carving out an appropriate role for a sitting judge, I think for that very reason the cleaner answer is to seek a retired judge who is no longer part of the judiciary.
The problem is that this person, she or he, will be serving in the executive branch as a sitting member of the judicial branch, and that crossover raises even the perception of a conflict of interest that's systematic. Therefore, retired judges would be much preferable and there is no shortage of retired, talented judges who could fill these roles.