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.
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. :(