Heating in the buns shed.

With cookie being a disabled bun I really need to get some heating in the shed as soon as possible. I find his head tilt is worse when it's cold. He does have a wifey bun but she tends to sit on the wooden box where cookie can't jump on. It's not even as if I can take the box out because it's where I store my hay. How would we go about adding a heated radiator?

could you fix one quite high up where they wont be able to get to?
i dont really know what else to suggest sorry.