I would suggest installing the new version of glib under `/usr/local/lib` or `/usr/local/lib64` and then utilizing the `LD_LIBRARY_PATH` environment variable, like you mentioned above.
In fact that appears to be the default location. From the output of `./configure --help` in glib-2.33.8:
By default, `make install' will install all the files in
`/usr/local/bin', `/usr/local/lib' etc. You can specify
an installation prefix other than `/usr/local' using `--prefix',
for instance `--prefix=$HOME'.
See this Ubuntu Forum thread for more details.