

If its the former, the instructions below for holding the power switch in the on position likely work, some people seem to have confirmed it, if its the latter, then probably not. From comments, its not clear if this new design is a momentary contact switch (you slide it and it returns to the neutral position itself), or it locks into the on position, and must be manually moved back to the off position.

Apple Magic Keyboard: Apple revamped the bluetooth keyboard and rebranded it ‘Apple Magic Keyboard’ in 2015, and they change the power switch from a circular ‘momentary’ contact switch on the edge of the keyboard to a losing shaped slide switch on the back edge.
