Do you know those countersink drill bit sets with the drill bit and a four-tooth cutter head at the bottom? Take the cutter head off and attach it to a short-handled Phillips screwdriver so that the teeth are well above the Phillips head bit. SCrew tight the set screw and viola!
The trick is to push it against the stummel where you want it rusticated and twist. Just use a lighter touch, this thing really cuts the wood if you want it to! (My first rustication was quite gnarly with it). You can always go back over the area with a bit more pressure, but once cut too deep its a done deal.
"Governments may think and say as they like, but force cannot be eliminated, and it is the only real and unanswerable power. We are told that the pen is mightier than the sword, but I know which of these weapons I would choose."~Sir Adrian