Here's the clip:
http://idisk.mac.com/doctorvague/Public/Clips/Road_Apples_of_the_Moon.mp3

Osc 2 sine > Osc 1 softsync input set at 3-8 (play with this)
Osc 2 was fed some notes from a Monopoly arpeggiator but you can use a sequencer or play real time
Noise > S&H > Osc 1 1/V oct input. I triggered the S&H with the Monopoly gate out so each note is different.
Fast EG with no or low sustain to State Variable filter cutoff
A moderate amount of S&H output also sent to filter cutoff
Osc 1 and Osc 2 > mixer > SVF audio input (use mostly Osc 1) I believe I used a fairly narrow pulse out on both osc.
SVF output to VCA
Fast envelope with low or no sustain to VCA control input
VCA > audio out

The trick (beside using the softsync in its middle range) is to find the exact envelope settings. It needs to be fast but vactrols have "ring" and also "thwip", meaning they don't come on or shut off instantly, even hit with a square wave CV, so the envelope attacks have to be very slightly higher than zero to imitate with a regular envelope/filter/VCA- just one or two tick marks up from zero. You can use a small amount of sustain and short decay and release (but longer than the attacks), i.e. settings around 1-2.

A vactrol is a trade name for a device that has both an LED and a photocell in one pkg. They are light coupled but not electrically coupled. The photocell has a slight lag time coming on and an even longer lag time to shut off (known as 'ring"). These lag characteristics  are known to be musical so they are used in things like Buchla Low Pass gates, but also in classic compressor designs - wherever you see "opto" in the name or description.