I guess for Britain to be amenable to peace, you would need Halifax as PM instead of Churchill.
Halifax was only "amenable to peace" with Hitler in the same sense that the British were
"amenable to peace" with Napoleon in 1802. In truth, Halifax hated Hitler as much as Churchill and by no means would have just lain back and acquiesced to Nazi dominance of the continent. While Halifax would have accepted a generous peace, there is no chance he would have signed a surrender. The British would have followed the same practice they used in the Napoleonic wars: sullenly retreat back to their island with the loss of their continental allies, build up their military, and then restart the war once Hitler looked vulnerable (that is, once he attacked the USSR). All Hitler would have bought himself with a favorable peace with Britain would have been a short respite during which the British would have continued frantically re-arming, while looking for any opportunity to plunge in the knife.
Just have France and Britain allow Germany to take control of Poland and dissolve the state. Hitler will come to dominate eastern Europe and eventually invade the Soviet Union early in 1941. Britain and France are not involved in any war with the Germans and stay out of the conflict all together.
Chances are that if the Allies don't declare war over Poland, Hitler invades France in the spring of 1940 anyway. If one actually reads Mein Kampf (which I admit is a difficult thing to propose... Hitler was a lot of things but a good writer was not one of them), Hitler lays into the French as much as he lays into the Russians, calling the French the natural enemies of the Germans and stating flatly that they'd have to be crushed before Germany could achieve her destiny. Militarily, he actually portrays Russia as an afterthought - a bankrupt regime of cultureless barbarians squatting in the ruins of a civilization whose only greatness was transplanted onto it by its now usurped ruling class (Hitler was fond of pointing to all the German blood in the Czars). Hitler actually wanted to invade France immediately after the war with Poland, and was only stopped by his horrified generals stalling until winter arrived. It's pretty clear that whatever his immediate reaction might have been to the Allies' declarations of war (it appears the Ribbentrop and some of the military leadership had fooled themselves into thinking the Allies would back down again), Hitler had been itching to have a go at France for years.
Hitler was also fully aware of the increasing pace of French re-armament, something he harangued his generals with repeatedly in October of 1939 when they pleaded with him for more time to rest and plan. Basically, so long as France was mobilizing and re-arming, Hitler was always going to push to attack them as soon as possible. He is not going to take on the Soviet Union while leaving the re-arming Anglo-French to his rear.
I do question however if the Soviets, on their own, could defeat Germany. Without Lend Lease, which I am assuming we are butterflying, as Britain out of the war means that Churchill and the like still see the Nazis and Soviets as equally awful enemies, the Soviets might have starved and certainly would have lacked the vehicular transport to carry out big offensives.
Without the looting of Western Europe, Germany's logistical capabilities for Barbarossa are essentially cut in half and they will be unable to penetrate into the Soviet interior. Without a war in the west, Stalin is much less liable to be taken by surprise thereby drastically increasing the difficulty of the fight for the Germans from the outset. Barbarossa likely stumbles to a halt west of the D'niepr river line, leaving the Soviets with the economic-military resources to crush the Germans by 1944 with or without lend-lease.
That being said, the utter lack of destruction of German industry and infrastructure caused by no WAllies and their blockade and air force might have evened the score.
Not when Germany's dire financial straits, the lack of loot from the West, and the greater failure of Barbarossa leaves them facing the same raw material crunches as IOTL and even worse manpower crunches. Meanwhile, Soviet productive capabilities will be massively boosted by the retention of so much equipment, industry, raw materials, manpower, and farmland that IOTL was lost to the Germans.