Since neither a computer nor a speaker system is designed to provide a safe electrical source for connecting to the body, I would avoid trying either. No one wants to be the news story of being electrocuted by hooking themselves up to a stereo or computer. I also do not think that it is a great honor to win the Darwin Award.
You can easily and cheaply build a manually operated BBBE with 3 batteries, a couple of resistors, and a toggle switch.
There are instructions on the internet for this, as well as for ones with a op-amp output.