Any LLVM bitcode converter to downgrade bitcode across main versions

Hi mailing list,

Is there any tool available for downgrading LLVM bitcode to a lower version (such as LLVM 3.x → LLVM 2.x)? I need to use a symbolic execution tool (supporting only LLVM 2.7) to analyze a code base that contains some c++11 features. But I am facing some problem: I can use clang 1.1 to generate LLVM 2.7 but clang 1.1 does not support c+11; using a newer version of clang that supports c++11 (such as clang 3.3) will only generate LLVM bitcode of version newer than LLVM 2.7.
So I am wondering if any LLVM pass or tool exists in the LLVM community for converting LLVM 3.3 bitcode to LLVM 2.7 bitcode. I found some discussion ( of LLVM bc converter for downgrading bitcode, but seems like it only supports downgrading within one main version (such as 3.x).