Honestly, I don’t know the answer to the situation in which cremation supercedes the presence of the body at liturgy. Lacking any theological, liturgical, or pastoral reflection, there’s no real place for the growth of the clergy, ministers, mourners, and the faithful. Maybe this avoidance of death in our culture is too deeply embedded in us.
Anyway, cremation is permitted by indult, and certain preparations are needed:
427. If the diocesan bishop has decided to allow the celebration of the Funeral Liturgy in the presence of the cremated remains of the deceased person, care must be taken that all is carried out with due decorum. The cremated remains of the body are to be placed in a worthy vessel. A small table or stand is to be prepared for them at the place normally occupied by the coffin. The vessel containing the cremated remains may be carried to its place in the entrance procession or may be placed on this table or stand sometime before the liturgy begins.
This makes good sense. A “worthy vessel” is not as weighty, literally, as a casket. But it needs to be treated as such.