Here's the deal. I finally got diplomacy and I launched a single player game. I set a map designed by myself, which looks pretty much like a little enlarged version of the Huge Single Star random map. I set unlocked teams (gotta check the diplomacy rite?), turned off the pirates (I've read enough about these lads, thank you ) and picked 6 AIs. I grouped the AIs in pairs (one with me and then two more pairs). One AI was left, so I made him Cruel and left him alone.

Obviously, Murphy's laws took place and the Cruel AI, with the worst of intentions, landed just three jumps away from me and the only good chokepoint between us was a magnetic cloud (orky's lost the job in this case). Anyway, just after the game started, the cruel AI decided I was having too much fun and started pounding on me.

Our relations plummeted and ended up somewhere in the -7.5 neighborhood (only negative factors from military actions, military strength, diplomatical inclination, racial inclination modifiers).

Question is - how do I use the tools from diplomacy to break the cuel AI's bloodlust?
Gifts seem to only bring the relations up by 1 point. My envoy cruisers in the magnetic cloud are welcomed with a beautiful bouquet of missiles, so planting them in the magnetic cloud is out of the question, planting them anywhere further even more so. I can manage to make 3 points from the passive boost researches and 1.5 from a silly "gimme 1k credits" mission. However, altogether this is 5.5 points and our relations are still solidly negative.
What else could I do?