How do I see the command line equivalent of clicking Verify?
In the Arduino IDE switch on File>Preferences>Upload erbose and Compile Verbose

When you build you will see all the compiler commands

The verify is often a -v param in the command

You will find the esp8266 platform.txt in a location such as c:\users\[name]\appdata\local\arduino15\packages\esp8266...

The platform.txt contains all the compiler switches, the boards.txt in the same location can also contain board specific switches.

You can not specify different switches for different files in a compilation but you could compile your code into an archive then force it into the build process. Not sure if that is practical or not.