如何在virtualenv中安装python3-gi？

我正在遵循Python GTK + 3教程，并且试图在virtualenv中运行有效的安装。我已经通过Ubuntu软件包管理器安装了python3-gi。事情看起来像这样：

:~$ mkvirtualenv py3 --python=/usr/bin/python3
Running virtualenv with interpreter /usr/bin/python3
Using base prefix '/usr'
New python executable in py3/bin/python3
Also creating executable in py3/bin/python
Installing setuptools, pip...python
done.
(py3):~$ python
Python 3.4.0 (default, Apr 11 2014, 13:05:11) 
[GCC 4.8.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import gi
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named 'gi'
>>> 
(py3):~$ deactivate
:~$ /usr/bin/python3
Python 3.4.0 (default, Apr 11 2014, 13:05:11) 
[GCC 4.8.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import gi
>>> 

如您所见，python3-gi在virtualenv中显然不可用，但是我不确定如何安装它，因为python3-gi是通过我的包管理器而不是pip安装的。