High voltage Capacitor Discharge Tool
Any sane designs that use high voltage capacitors have bleed resistors across them. So as a precaution let the device under test sit without power for a while before probing, then proceed with your "tool". 

I just use a long insulated screwdriver to short the capacitor. Proceed at your own risk ofcourse. 

Just remember, shorting a large capacitor unleashes a lot of power and give off sparks and huge bang.

PS: i was reluctant to present this as a answer as opposed to a comment because i dont want a quick browser to think this is the way to go. Again, be very careful!