I did it on 'challenging', Arcean intelligent, others set on bright. Coupled with +5%PQ and +weapons, Tiny map. Kept Drengin (second race to encounter) at 'warm+', even with their military 2 times higher, no demands at all. Were the last to be conquered. Since I play mostly Tiny maps, this trade bonus is quite handy unless I want fast conquest. One game as Universalists (Painful) with slight bonus in trade was rather easy as well. Me, being 'good', had 'close' relations with Altarians and Torians, and 'friendly' with Drengin (default alignment for all races), till I attacked last. After making peace treaty, relations returned to 'normal' within few monthes.
+trade and mercantilists keeps others on good terms with you even if there is only one trade route between nations (at least, on Tiny). I also start selling all techs to every single race I encounter for small sum for long time, it could be the case why my relations are rather good/neutral with everyone till I attack them. Dunno if it will work on Genius/Incredible AI, will try in time.