You can't (well...you can probably constrain the high/low swings with some command line option). Ogg

was designed as a VBR format. If your looking for a 192 kbs average then I would encode at -q 5 to -q 6. But it is highly dependent on the material your encoding....the kbs swings are much greater than any other format I've seen, making it much harder to pin down an average rate (but that's one reason it sounds sooooo good

). Accept no substitutes.
xen-uno