Attach one end of the spring (proably to the sidestand end), then loop the other end of the spring over a stout phillips head screw driver. Lay the point of the screw driver over the other attach post. Postion the screw driver so that the attach post is nestled in the cross of the tip. Then just lever the spring into place. The spring will slide down the screwdriver shaft and slide right onto the post. First time is a little hard trying to figure the angles, but once you get the hang of it, it's a 15 second job. I have an old screw driver in my tool box just for that job.
The washer trick works best when you think to insert the washers before you take the spring off. And it takes longer too.