This week I created scripts to install gcc-4.8.3 and gcc-4.9.1 with boost 1.56. Here is the simple Makefile.
These scripts are also available on github:
https://github.com/jlinoff/gcc-4.8.3-boost-1.56
https://github.com/jlinoff/gcc-4.9.1-boost-1.56
https://github.com/jlinoff/gcc-4.8.3-boost-1.56
https://github.com/jlinoff/gcc-4.9.1-boost-1.56
Enjoy!