Is there a way to add a widget in the middle of some editable content?
I would start by looking at the following;
This would allow you to create a tag that could be used in the content area to call in your widget. Then you would probably also need to create a method on a Page class to manually create your widget as there will be no Widget area as such. See the following for details of how to do that... (the Rendering a $Widget Individually bit)
Never done this myself, but this is where I would start looking.... not the easiest, hopefully someone else will post an obviously easier way that I don't know about!