Upgrading a single package is often not a problem. Upgrading `libc` _will_ be. There are simply too many other packages that depend on it:

    $ apt-cache rdepends libc6 |wc
    16057

That means that 16057 other packages will depend on `libc6` and some of them are bound to have problems with the new version. That's one of the main benefits of a packaging system.

So, you don't want to upgrade that without upgrading the rest of your system. What you _could_ do is create a `chroot` environment and install a minimal distribution there. For details on how to do that, have a look at @Gille's answers here:

* http://unix.stackexchange.com/questions/12522/installing-two-glibc-alongside-in-debian-ubuntu
* http://unix.stackexchange.com/questions/12956/how-do-i-run-32-bit-programs-on-a-64-bit-ubuntu/12957#12957