Yes it's possible. I managed to control a servo via a parallel port. The main thing to note is that the ground wire (usually the black one) has to go to both the negative terminal of the battery, and the ground pin of the parallel port. That little subtlety took me days to figure out.
So basically, the control wire is wired to a digital pin of the parallel port, the power + goes to a battery, and the ground goes to the ground of the parallel port, and the - of the battery. Then, by varying the pulse width, you can control the servo's position.
However, I noticed that it is somewhat difficult to get the computer to create accurate pulse widths, so you might notice the servo twitching generally. I couldn't find any way around that and so I bought a servo controller board ultimately.
