I tried placing the completion script in that directory but it was not automatically sourced for me. Do you have something extra setup in your `.bashrc` or `.bash_profile`? Or maybe your `bash_completion` script in `/usr/share/bash-completion` automatically sources that directory for you.

The two available directories on my system that allow for automatic completion loading are:
```
/etc/bash_completion.d
/usr/share/bash-completion/completions
```
(run `pkg-config --variable=compatdir bash-completion; pkg-config --variable=completionsdir bash-completion` to see what they are for you - [`bash` FAQ](http://anonscm.debian.org/gitweb/?p=bash-completion/bash-completion.git;a=blob_plain;f=README)).

Lastly, installing things to `/usr/local` still requires `sudo` on my machines.