So Stalin decides it would be better to have Socialism in one country, and does away with the nominal independence of conquered territories. As a sweetener, he may offer increased autonomy to the various SSRs as well as drastically limit or even give up on the reparations to be paid. Also in the works is an earlier, almost immediate frosting of relations with the west - where the Red Army Soldier sets foot, communism follows
As to the map:
Greek SSR - Hitler decides not to allow his Balkan garrisons to withdraw, hoping to turn the situation around. Thus, most of Greece is liberated by the Red Army, which proceeds to empower the leftist guerrillas. Most islands and the Morea peninsula form the Kingdom of Greece, under British protection.
Austrian SSR - the Red Army took over Vienna and most of eastern Austria in the closing days of WW2. After disagreements with the Anglo-Americans, no transfer of territory takes place, and eastern Austria gets to enjoy the warm embrace of Mother Russia
Czecho-Slovak SSR - The Prague Offensive was the last major battle of WW2 in Europe, taking place after the official surrender of Nazi Germany, and it saw most of Bohemia liberated by the Red Army and its allies. US troops however had also reached most of the Sudetenland in the west, from where they haven't left since.
German SSR - After Hitler's last hoorah at the battle of Berlin, the capital and most of the surrounding area came under soviet occupation. Plans had been laid out for the western half of Berlin to be transferred to the allies in return for Thuringia and Saxony, but increased tensions saw the border stay in place
Norwegian SSR - the last organized Nazi resistance to take place in Europe was witnessed at Narvik, where the local German garrison was hoping to surrender to the Allies and not to the small expeditionary force the Soviets had scraped together. Despite weeks of vicious resistance, the Germans were eventually overcome by the continuous arrival of Soviet reinforcements. Following this victory, a revolutionary government was installed in the burned out ruins of Narvik.
Finnish SSR - The last European SSR to be admitted into the Union. The Finns were reluctant at first, but the half a million strong Soviet occupation force eventually convinced them to see the error of their former ways.
Iranian SSR - Soviet and Western Allied forces were supposed to have both been withdrawn from Iran. Fortunately for the landless Iranian peasants, that never happened, as the Soviets liberated them from their oppressive landlords and brought Socialism to them
Ainu SSR - Whilst the Americans were busy with Downfall in the South, Soviet forces managed to get a foothold in Hokkaido before Tokyo finally threw in the towel. What followed was the the liberation of the oppressed Ainu people, who got their own state (including Sakhalin and the Kuriles) within the brotherhood of socialist peoples.
Manchurian SSR - In a beautifully orchestrated offensive, the Red Army mopped the floor with the IJN in the final months of WW2. Despite the failure of Mao and his communists in China proper, Stalin was not about to give up land to the American puppet in Chongqing, and so set about integrating Manchuria into the Union. Parts of it went to the Korean and Mongolian SSRs, depending on the ethnic make-up of the population
Mongolian SSR - got bits of Manchuria and northern China that were inhabited by ethnic Mongols, as well as the protection of the glorious Red Army from the oppressive and decadent Koumintang in the south.
Korean SSR - liberated by comrade Stalin (who kicked out the last remaining Imperial Japanese forces in mainland Asia), governed by comrade Kim. Hopes to one day kick the evil American imperialists and their puppets out of Jeju island.
Xinjiang SSR - ever since their invasion in 1934, Red Army forces had been stationed in the region. After the loss suffered by their socialist comrades in the Civil War against the Koumintang, Stalin decided accepting them into the Union was the best way to keep them safe
Tibetan SSR - With the risk of an Imperialist aggression imminent, comrade Stalin decided that it was time to liberate the people of Tibet from their theocratic rulers and bring them into the 20th century