The last paragraph of your question is misleading, at least for me. If your goal is to find a way to invoke
service as user
Phing without getting asked for a passphrase I would do it with
sudo. I will try to answer you question as I understand it, since I don't grasp what speak against the use of
sudo in your case.
Just add the line
/etc/sudoers. This line adds the user
Phing to a group on which
sudo doesn't lay down path and password requirements.
Further you have to add the line
Phing ALL=(root) /full/path/to/service
or alter an existing line of
Phing, so that
sudo grants him access to
sudo service php5-fpm restart
Phing for a passphrase any longer.
If you want it a bit more strict you can instead add the line
Phing ALL=(root) NOPASSWD: /full/path/to/service
exempt_group. Then you have to give
sudo the full path of
service (if it's not located in the standard paths), so command spoofing isn't possible.
If you want to save some typing, you can also alias
sudo service or
sudo /full/path/to/service in your shell with