I think it's been done though it's not easy I suspect. I recently saw a quote though that NO baryancistrus had been bred in captivity but I am sure I've heard reports. I think you need a pretty high water flow, warm, soft, slightly acid water, very well oxygenated. The only comment I have heard on this subject was something along the lines of 'bred in a flowerpot cave, when a powerhead was pointing right at the spawning spot.
I would imagine it is possible, and as I think nuggets are my favourite plec, am thinking about trying it myself. I think you'll need the above, in a large though not enormous tank, no other fish to pinch food, and feed a lot of shrimp, bloodworms and other meaty goodies. You'll also need patience as I'm sure these things need a few years to grow and mature. Once you've got a few I'm sure sexing will be obvious by vent shape.
Ask on planetcatfish forum boards, and good luck. A trip to the biotope would help, as would internet searches (repeated on different enines) on the words baryancistrus breeding in english and german.
Get some combat experience with other plecs first, obviously.