late in the game I have been prostituting myself by going to war with a minor like i-league or da fundies, only to offer peace and in exchange for his far-flung planets. Following a blog on "mercinary" I offered war free of charge to a major who was at war with the minor. What a diplo coup! I went up about 3 grades! I tried it again just to see, and the same thing. Wow. Going to war with a minor has about zero disadvantages, but offering war, reaping the diplo, then offering peace seems way too good.
Please don't tell me this is a new cheese, 'cause I'm just not a happy cow.
The reason for the dramatic diplo improvement is really the same behind that of the Tiny Tribute cheese -the effect of massive diplo superiority through loading up on diplo picks.