Share a screenshot with the Facebook SDK on WebGL

(This has been asked before but has never been answered properly)

I am trying to create a webgl app that can share a screenshot to facebook. Using the facebook SDK there is an example script here that shows you how to share an image to facebook. The problem with this example is that it fails the facebook app review process because this method "auto-populates the user message field" and also "does not use the Facebook Feed Dialog or the Facebook Share Dialog to publish content".

If I instead try to use the feed share functionality I can't get it to work as I cannot share a file created locally. (I tried this solution but it failed as I couldn't share a photo on their own feed. Also I'm still posting that image to the users feed first without any confirmation, so it would fail review anyway)

The only way seems to be by hosted the screenshot on a website, but I'm not a web developer and don't really know how to create a screenshot and then host it somewhere else, so this is a less than ideal solution.

It seems like a trivial problem, but yet I cannot seem to find a solution online. It also strikes me as weird that their example code fails their own review process. Can anyone help me?