All you have to do is get your violin to make a harmonicly rich sound and run it through an analog filter.
Here's how: 1-Plug the output of your violin into a distortion effect. This will add harmonics to your sound making it buzzier and more like a square wave. This step is important as most analog synths' oscilators create bright buzzy waves.
2-Get an analog filter module NOT a rackmount Synth since you dont plan on using MIDI. I suggest a Waldorf 4-pole or X-pole. Plug the out of Distortion into it, and experiment.
- DON'T buy a rackmount sythesizer like a JP8080 if you're not going to use MIDI. It is a complete waste of money. Also try a Mutron or Q-tron (effect pedals that are filters) and there is a BOSS pedal that makes synth sounds by tarcking the pitch of its input.
By the way MIDI rocks. You really should learn more about it. I've heard of violinists using MIDI. Also, ask a friendly keyboardist with an analog synth to show you how it makes sound. Education is the key to accurate emulation.
Email me if you have questions
-peace