I did something similar: http://www.fieldlines.com/comments/2004/2/12/103922/657/4#4

I can't tell for sure how large your stepper motor is, but it may be similar to the ones I've fiddled with.  With my best stepper motor, a voltage doubler on the output, using the plastic fan blades shown in the link above, in a gusty Oklahoma wind, I got less than a 1/2 Watt into a 75 Ohm load.  The voltage doubler probably added a little loss to it and wasn't of any use to the 75 Ohm load, so it maybe could do better.

In your application, you could take the AC out, run it throught a step-up-up-up transformer to get the right volts and you might get a few microamps into an electric fence (which might be all you need).  Alternatively, you could use voltage doublers to get to the final desired voltage and pulse that into the fence.

I'm planning to prove whether or not I can use my setup to pulse charge some smallish Sealed Lead-Acid (SLA) UPS batteries.

Nice job on the blades.  You did good work for just a few hours invested.