Brezhnev and his closest cohorts get sidelined in favor of more pro-reform leadership in the 1960s Kremlin - pretty much required. One potential alternative leader to Brezhnev was Alexei Kosygin, who advocated for continued reforms and more emphasis on consumer goods but got such proposals rejected or reduced in scope. That, and/or Czechoslovakia's 1968 Action Program is actually carried out, then spreads from there to the rest of the Warsaw Pact. State monopolies become supplemented by "workers' cooperatives" and semi-public enterprises, which are given greater chances to conduct trade with other 2nd World countries.
If China avoids the Sino-Soviet Split or decides to pursue some rapprochement with the Eastern Bloc post-Mao, that'd offer an opportunity for the economies of Eastern Europe to expand operations in East Asia. Alternatively, India may be open to such investment during this time period, thanks to their friendly ties with the Soviet Union. This may have the consequence of reducing industrial employment in the Warsaw Pact, but would also provide incentive for more service-sector activity.
Long-term idea: in response to the EEC/EU, Warsaw Pact countries counter with their own improved regional integration programs and easing of trade/travel barriers within their bloc.