I'm thankful this type of problem hasn't come by my desk so far, but at this stage in the game I would assume that there would be a number of mature libraries for doing the ie8 iframe shuffle. I wonder why they went with a custom solution.
Actually, I don't know of a single ie8 frame communication library. Most are part of bigger libraries and we were trying to keep things slim.
I found three when I had to do this. None of them worked correctly, and the JQuery plugin I found had a very poor API. I ended up writing my own, because the bar set by the existing software was so low.
Filepicker.io was one of the ones I looked at, and I still think my implementation was better.
I wish I had smuggled a copy of it out of that company before I was laid off. :(
After going down a rat hole of implementing a cross browser file input recently, with transparent overlays and special iframes and all that jazz... definitely will be looking to use filepicker in my next project that needs it.