Here's an idea... I'm not 100% sure how the Armistice autocast works, but it might only activate when the Akkan itself is damaged. If you turn all autoattack off on all ships and strikecraft, and then priority target one enemy Akkan, it will quickly Armistice - but that will expire after 60 (ingame) seconds and you might be able to then manually order everything to shoot at it and it may die. Repeat for all enemy Akkans and then you're down to a standard fleet-to-fleet battle... if your fleet is superior you can then just sit back and watch the fireworks.
Of course, if Armstice AI-autocast activates even when the Akkan itself isn't being damaged, this won't work...
Another idea which should work regardless: split your main fleet. If Armstice keeps getting activated, you aren't in much danger of losing many ships yourself in that main battle: you could send all your Ogrovs or carriers/bombers, plus a few siege frigates, to other enemy worlds. The AI is very bad at splitting its fleet efficiently and quickly: simply warp out to another world when the enemy warps in. If you can do this on 2 or 3 fronts that'll probably spell death for the AI, if you can respond in time (shouldn't be a problem given the LONG time everything takes).