Just want to say, I repair digital cameras for a living. We have audible dischargers. There is a few resistors and a speaker. It generally takes like 3 seconds to discharge a flash cap, and with an audible discharger, you pretty much know when its discharged. I say pretty much because even though you may think the noise has stopped, it has really just become so quiet that you dont hear it. So after using a discharger you can then use a screwdriver (or whatever) to make sure. This will result in a small static like spark (if anything), as opposed to the virtual explosion that happens when you short a fully charged flash cap.
I have to imagine that these dischargers are cheap enough to be worth purchasing one, but if you are going to make your own, I definitely would want it to be an audible style.