Yes, GM Passkey II is a joke. You can in fact just bypass with putting a resistor in-line that matches key. My Olds Aurora has this system as well. I don't see why anyone would tap into actual ignition wires on the column when switched ignition wire power is readily and more easily available in many other places. One source as mentioned twice in thread already is from the stock radio harness. Which can be utilized by using after market harness and makes for great easy hookup to after market 4 channel amp.
Also, I wouldn't see needing a solder gun unless you are using larger gauge wire. A standard solder iron will work fine with most smaller gauge wiring used in these CarPC applications.
I guess what this is boiling to as it does with many arguments is...it's your car do as you please,if you are doing it for someone else do it the right way. However, it's just easier to do it thr right way the first time, eh?