Chiming in a bit late, but if you plan to paint it anyway, you might just consider sanding down the rough edge, using a shop vac to get all the dust out, then running over it with "whipped joint compound" (it's reg joint compound only the consistency of whipped cream). NOT HEAVY, just enough to fill the tiny crevasses. Sand it down again, and you should have a pretty smooth edge. The problem with this is that the joint compound is not very flexable so it will break out if you put it on heavy when the machine flexes. On the other hand if you are just using it like wood filler and use very little, you should be fine. Don't skimp on the paint either, and it should lay on a bit smoother. Not exactly what your looking for it sounds like, but maybe it will give you the look you need.
On another note, I didn't route my cab until assembled either. A bit tougher and I had to do the horizontal sections (at the ends anyway) with a razor knife, but I did managed to pull it off without it looking totally armature.