Just stick your tongue across the caps. That should work, and it won't kill you. You might feel a slight pinch, to quote the nurse who shoves the horse-needle into your backside.
Joking aside, I would use a simple high-value resistor connected to a couple of insulated leads and some kind of small connecting clips to discharge the various caps that hold a high voltage. This isn't specific to your amp, just a general good rule to follow in any circuit needing to be discharged. Determine the highest volytage you'll see, and use a resistor calculated to #1 keep the current under a lethal value, and #2, not exceed your resistor's power rating.