Hi,
there is nor spezialized tool yet but you can easily work around. Just do the following:
1. Select some polygons.
2. Delete these polygons with the "<--" key.
3. Chose the "Fill Hole" tool and move the mouse cursor over a point which is on the edge of the hole. That point will be highligthed in violet. Finally click on that point.
4. Your done. A nice n-gon has been created.
By,
Martin