So, did a search on the thread and was amazingly surprised no one has suggested doing method 2 with a simple push-button (always open unless depressed) "latching relay". This gives you simplified install while also working with timer control. The push button is only to engage the relay, that can only be powered while the car is on. That closes the circuit for the 330ohm resistor. When the power goes off, the relay disengages and you are back to stock wiring and ready to engage climate control timer. Way, WAY easier than method 3. You can also get fancy and buy an illuminated switch that is wired to the relay power to have a visual indicator of on or off.
If your not familiar with a latching relay, basically you use the 12v power that would be used to power the switch also loop through the relay switch and back to the coil +, that once engaged, keeps the relay on. The relay will not disengage until 12v supply is lost (car off). if you want to manually disengage the relay, you install a normally closed push-button switch that temporarily breaks the 12v supply to the relay. Normally closed push-button switches are always closed while disengaged, and broken only while your finger is depressing.
So effectively, you have the best of both worlds without the solder and loss of time.