building llvm-gcc4 with an installed version of llvm

llvm-gcc4 currently references some files from the build directory of llvm, but looking through the make file, I haven't yet come across a file that llvm-gcc4 needs that isn't installed with llvm. I checked, and all the headers for the src and obj are installed into ${prefix}/include/llvm and ${prefix}/include/llvm-c. All the main object files are the same as well. The only difference with binaries are that these aren't installed: fpcmp, llvm-PerfectShuffle, and tblgen.

If this is the case, would it be possible to add something to llvm-gcc4's configure and Makefile to support building based solely off of a specified llvm-config?