The Church makes a strong case for the celebration of viaticum at Mass:
177. Whenever it is possible, the dying Christian should be able to receive viaticum within Mass. In this way he or she shares fully, during the final moments of this life, in the Eucharistic sacrifice, which proclaims the Lord’s own passing through death to life. However, circumstances, such as confinement to a hospital ward or the very emergency which makes death imminent, may frequently make the complete Eucharistic celebration impossible. In this case, the rite for viaticum outside Mass is appropriate. The minister should wear attire appropriate to this ministry.
178. Because the celebration of viaticum ordinarily takes place in the limited circumstances of the home, a hospital, or other institution, the simplifications of the rite for Masses in small gatherings may be appropriate. Depending on the condition of the dying person, every effort should be made to involve him or her, the family, friends, and other members of the local community in the planning and celebration. Appropriate readings, prayers, and songs will help to foster the full participation of all. Because of this concern for participation, the minister should ensure that viaticum is celebrated while the dying person is still able to take part and respond.
The celebration of Mass, even in the home of a dying person, provides for a richer connection to the Lord’s own death, richer than a communion service. The priest’s own convenience is not mentioned among these conditions for when this preference may or should be abrogated. Appropriate choices are governed by the situation of the dying Christian and the surroundings. This isn’t to say that a priest shouldn’t or can’t adapt the Mass to the circumstances.
Note two prominent post-conciliar principles advocated in PCS 178. First, that lay people should be involved in the preparation of the viaticum liturgy, especially the dying person, loved ones, and even the parish community. Second, note yet another emphasis on the importance of participation.