The "soft" switch is your friend, don't bypass it, allow it to do the work for you.
Easiest way is to relocate the "soft" switch (really a momentary contact switch, an arcade button and it's microswitch are perfect replacements). Mount the arcade button in a discrete location, pull the original case switch wire off the motherboard and wire the new arcade button in it's place. I used a 2 wire spdif cable, cut one end off, stripped the wires and extended them to reach the contacts on the microswitch. Connect to NO and Ground. The other end with it's original connector will fit the motherboard location perfectly, just like the original case switch.
Next, get one of the "smart" power strips. Plug the PC into the control outlet and eveything else into the switched outlets.
You can now turn the computer on with the arcade button and when the smart power strip sees that the computer is on it turns on everything else.
If you are running win98 or higher, briefly pressing (don't hold) the computer power button will tell windows to do a proper shutdown (just like if you clicked start -> shutdown) and power off the computer. When the smart power strip sees the computer is off, it will turn off everything else.
This method is preferrable because it allows the computer to startup and shutdown properly, the way it was designed to.
You can get the smart power strip at sears or from an online retailer...