I have created a PPA that contains a build of GCC 4.7 for Precise here:
ppa:george-edison55/gcc4.7-precise (Click here for instructions on using PPAs.)
To backport a package from one release to another is a relatively simple process assuming you have a Launchpad account and have registered your GPG key there.
Make sure you have the ubuntu-dev-tools package installed:
sudo apt-get install ubuntu-dev-tools
The syntax for running the backport command looks something like this:
backportpackage -s [new_release] -d [old_release] -u [ppa] [package_name]
The command above will backport
[old_release]and upload it to
[ppa]. Note that in this particular case you will need to backport not only
gcc-4.7 but also
gcc-defaults in that order.