Modifying GCC's default search dirs

[Shaun Jackman <sjackman at gmail dot com>]

I would like to change GCC's concept of its PREFIX and MACHINE, for
the purpose of modifying GCC's default search directories. For
example, my local GCC was configured with PREFIX=/usr and
MACHINE=i486-linux-gnu. I would like to tell GCC to instead use
PREFIX=/usr/local and MACHINE=i386-linux-newlib, so that the default
library search path includes PREFIX/MACHINE/lib and the default header
search path includes PREFIX/MACHINE/include. Is this possible?

I've run into the environment variables GCC_EXEC_PREFIX and
COMPILER_PATH as well as the switch -B. I've tried playing with these,
but they don't seem to have the exact effect I'm looking for. In
particular they seem to be adding additional search directories,
instead of replacing the default search directories.

I've also run into the -b MACHINE and -v VERSION switches which gave
me hope, but they only seem to call the binary MACHINE-gcc-VERSION,
which, if it doesn't exist, doesn't accomplish much of anything.

Thanks!
Shaun