Fastest method of support grinding? (Revelation)

[Roflolxp54]

After gathering route-exclusive supports from Birthright and Conquest, I'm currently working on gathering the bulk of the supports in my Revelation file. I'm at Chapter 14 with more than 30 hours clocked in.

I want to know if there's a truly efficient method for grinding supports outside of scouting random encounters (I often use Plains of Hoshido/Chapter 6 because of rather weak enemy units on one side of the battlefield at the start and Plains of Hoshido being largely an open area with no obstacles aside of some forest terrain).

It pretty much boils down to (assuming grinding for only a single pair of units):

-1 battle for C-rank support

-2 battles or 1 battle with Seed of Trust or random relationship improvement if medium growth; 1 battle if fast growth to go from C-rank to B-rank

-2 battles or 1 battle with Seed of Trust or random relationship improvement to go from B-rank to A-rank support

-2 battles to go from A-rank to S-rank

Is there a way to make this go faster? Sadly, event (sparkly) tiles are useless for this as they don't provide bonus support points unlike in Awakening.