I have replaced mine at least twice. Yes, the spring comes flying out, and yes it is a big pain to get it back in there. I did manage to do it though, although I don't remember exactly how.
One suggestion is to try putting in an extra long cord, and leave the spring as loose as you can when you put it back in. Then once it is assembled (with little or no spring tension) you can pull some of the cord out (winding the spring), cut it short, and put on the cord handle. This might be easier than starting with a normal length cord.
-Kevin