By Sinead Cruise and Tommy Wilkes LONDON (Reuters) – A Bank of England fix to ease pension schemes’ cash crunch by getting banks to assume the role of rescue lender is being shunned by some of the biggest banks, who say the returns on offer do not reward the risks involved, sources said. The BoE’s Temporary Expanded Collateral Repo Facility, launched on Oct. 10, is a key part of the central bank’s plan to avert further turmoil in money markets after it stops buying UK government bonds on Friday. Banks offering the facility can pledge an expanded range of pension funds’ assets with the BoE in r…