Hi Nick,
You can use a lathe to rewind the spring so it can be put in the housing. Start with a piece of suitable round stock and saw a slot in one end, chuck it up in the lathe,. Make another bit to hold the other end and place it in the tool post. slowly, by hand, using the chuck key, wind the spring, advancing the cross slide as necessary, until the cover will slip over it. Now release the spring slowly until it is captured inside the holder.
Joe