I wonder if there is some kind of noise generator that a small boat could carry that would repel, but not harm, enraged orcas. Maybe there's a whale equivalent of nails-on-chalkboard that would work without being loud enough to do damage or require too much energy to be practical.

If there is an attractive rather than repellent sound that would work (a calf in distress?) maybe it could lure the grampus away with a little remote control boat.

But their intelligence might make whatever does work only temporarily effective.