Maybe the drag-drop operation should open a scaled down "Open" dialog whenever the user tries to open new files in this way. I think I would prefer to do this with the help of a short-cut key by default (CTRL+DROP) for example. However, this could be configurable in application settings to make it the default.
The same dialog could be shown when a user tries to open a files via the OS. For example, by double-clicking on a *.log file.
Would this help?