How to make "cc1plus: error: unrecognized command line option" a warnings with -Werror?

Question

I have a project that is using gcc 4.6.3, and am trying to migrate to 4.8.2. However, it needs to compile on 4.6 for a while. It is using -Werror with a few specific errors turned off. To use boost 1.55 with gcc 4.8, i needed to add -Wno-unused-local-typedefs. The problem is that with -Werror, gcc 4.6 emits this error:

cc1plus: error: unrecognized command line option "-Wno-unused-local-typedefs" [-Werror]

The gcc docs on warning options have no indication this particular warning can be treated explicitly as a warnings rather than an error. Is there any way to get 4.6 to treat this as a warning?