Remove formatting on drag and drop

I'm working on an application using CKEditor where I would like to be quite strict on what kind of formatting I will allow the user to use. To achieve this I have set forcePasteAsPlainText to true. Unfortunantly,this has no effect when draging and droping elements into the editor.

I have found a partial solution, but it only works if the drag is initiated inside the browser window:

    document.addEventListener("dragstart", function(e) {
        var text = e.dataTransfer.getData("text/plain");
        e.dataTransfer.setData("text/html", text);
   });

It seems getData/setData is only available for the dragstart and drop event and when drag is initiated outside the browser window, dragstart is never fired. I've tried doing the text/plain conversion in the drop handler instead, but for some reason this doesn't have any effect.

Does anyone have a clue on how I should proceed?