I think I may have found a easy to use switch to trigger the Remote Shutter function in CHDK. On Amazon I found something described as
"Male to Female USB Cable with ON/OFF Switch - Easy Start/Reboot for Raspberry Pi & Arduino"
Theoretically, connecting this between the USB power output of a USB battery pack and the regular USB cable that connects to whatever camera you are using should give a power-on pulse using the built-in switch in the cable.
No soldering, monkeying with USB wires, or making/breaking the power connection is necessary with this cable.