seems the answer is in the comments and as an edit but to clarify this should work for you:
export BUILDDIR='your path to build directory here'
export SRCDIR='your path to source dir here'
export BOOST_ROOT="/opt/boost/boost_1_57_0"
export BOOST_INCLUDE="/opt/boost/boost-1.57.0/include"
export BOOST_LIBDIR="/opt/boost/boost-1.57.0/lib"
export BOOST_OPTS="-DBOOST_ROOT=${BOOST_ROOT} -DBOOST_INCLUDEDIR=${BOOST_INCLUDE} -DBOOST_LIBRARYDIR=${BOOST_LIBDIR}"
(cd ${BUILDDIR} && cmake ${BOOST_OPTS} ${SRCDIR})
you need to specify the arguments as command line arguments or you can use a toolchain file for that, but cmake will not touch your environment variables.