This may well be a custom where a bishop is serving at the Vigil for the Exaltation of the Cross, but the far more common and conventional practice is no less moving. Any choir worth its salt should be able to do justice to the troparion of the Cross Save, O God, Your people, which is arguably more evocative and more instructive than multiple renditions of Lord, have mercy in what is essentially a concert form.
In fact, the form according to centuries-old accepted practice is essentially the same as the Vigil of the eve of the third Sunday in Great Lent (also dedicated to the veneration of the Cross), and of the Vespers of Great Friday, where the burial shroud of Christ is brought out of the altar with great solemnity, accompanied by the Trisaghion hymn sung to the funeral melody. In the case of the Vespers of Great Friday, the troparion Noble Joseph is also sung, which is truly reverential and sublime. Not a dry eye in the house.