Girlfriend is gonna remodel her 2nd bathroom this spring. Meantime her

son has started using it for showers. Meantime when you pull the
diverter
thingy up, half the water still goes out the spout and down the drain.
That's
a lot of hot water being wasted, eh ? I know the spout unscrews from
the
pipe inside the wall for easy replacement. But I don't want to risk
causing a
leak inside the wall. Since the tub is used ONLY for showers, I'm
thinking
just plug it shut until she has the bathroom remodelled. So is there a
good
way to do this ?

thanks