Is there a way to let Android NDK-build use a newer version of gcc?
I believe your question would be answered by this NDK documentation: docs/STANDALONE-TOOLCHAIN.html. It sounds to me like you know what you're doing, so just heed the warnings and happy hacking. I believe section 3 "Invoking the compiler (the easy way)" is what you're looking for.
While trying to answer this myself I came across this, which is a step-by-step account of a man who successfully built the toolchain with GCC 4.6: http://glandium.org/blog/?p=2146.