GOD, I never played the variant, so I can't answer your concern (however, I was suggesting that the SU would enter after two years, i.e. in 1940, not in 1942).
Otherwise, I've come up with a more complicated time-frame to take into account that also Italy did not enter the war as soon as it started.
spring 1938: everybody holds
autumn 1938: everybody holds except Germany, who can move its armies (but not its fleet); furthermore, German troops can't move into territories bordering an allied power (for example, they can't take Switzerland).
spring 1939: war starts between Germany, Britain and France. These powers play normally, but 1) German troops can't enter Switzerland and territories bordering the Soviet Union, and 2) British/French troops can't move into territories bordering Italy (Cote d'Azur and territories in France proper are an exception). The Soviet Union holds. Italy can move, but can't enter territories bordering any allied power (except Turin).
fall 1939: the Soviet Union keeps holding; Italy joins the war. So, Italy, Germany, France and Britain play normally, except that Italian/German troops can't enter territories bordering the Soviet Union.
spring 1940: Soviet Union joins the war and all restrictions are lifted
let me know if you play because I'd be interested at looking at how the game evolves..