I think your problem can be solved using a simple symbolic link, but you are creating the symbolic link to the wrong file. As far as I know virtualenv is installed to /Library/Frameworks/Python.framework/Versions/2.7/bin/virtualenv
, (you can change the numbers for your Python version) so the command for creating the symbolic link should be:
ln -s /Library/Frameworks/Python.framework/Versions/2.7/bin/virtualenv /usr/local/bin/virtualenv