Or how about this:
The Soviet Union wins the propaganda war (or information war) against the US. The propaganda war was what the cold war mostly consisted of. So, what if the US discredited itself and the people of western europe stopped believing in US propaganda, instead believing in Soviet ones. Many people turn to the left, and the left turns more towards soviet-style socialism.
In the end, western capitalism is overthrown, and socialism becomes the worlds leading ideology. This would also make for a 'USSR wins cold war scenario'.
And for all that see this as too far fetched, a few things about OTL:
Many people in the 60s and 70s (not only leftists) saw the Soviet Union as the force for peace, and the US as war mongering (they had a point). Additionally, leftism was widely popular in the west, and communists like Che Guevara and Ho-Chi-Minh were the idols of the left in general. Many people (even high polliticians) wanted friendly relations with the USSR. People believed in the USSRs technological superiority (even more so before the american moon landing). And many people believed, that a planned economy was more efficient than a market economy, because of the USSRs higher GNP growth (especially during the 1967, 1973 and 1979 crises).
So its not hard to immagine a soviet edge in propaganda (especially as the soviets had major propaganda blowbacks, aswell).