Asynchronous Drag and Drop

Question

Hello,

I'm developing a piece of software which needs Drag and Drop functionality. It shows data available on a Document Management System. The user needs to be able to drag a file from my application to the desktop. The problem here is that when the file is large, it takes some time to download. In that time I do not want to block my user-interface. I cannot call the doDragDrop()-method in another thread because it needs the UI-thread.
Is there a solution for my problem?

Thanks for you help!