Can anyone confirm whether or not the steam.cfg method of forcing offline mode (see here) has been patched out? Last two times my internet dropped, I've tried to use this method to no avail, but it has worked for me in the past.

Last few times my net has dropped out and I've logged on to Steam it has started with no issues in Offline Mode.

I would try logging into the client in the normal way and then click Steam top left side and select go offline, it will restart the client in offline mode and stay that way as long as you just keep it minimised to tray.

I should imagine that link you posted will still work fine as it was posted up only a few days ago and there hasnt been any client updates in a few weeks now. Just make sure that you have your details stored like username and password before doing it (mentioned in linked post)