First is ok, as long as I can sufficient water to the screen, with an accessible control that is fine. Do yourself a favour and tell the tester that is what you have done, saves them hunting and thinking it doesn’t work if they know the way round your variety of vehicle. Second option is ok, as well, would look to wire it direct from a 12v feed rather than the cigarette lighter, as that is often used as an engine speed pickup for the emissions test, depending what order they do things in, it could cause you an issue.
Yes I am a nominated tester, otherwise known as an mot tester, or a fascist with a clipboard depending on your viewpoint on my profession.