How to create a flat surface across a hole in a cylinder?

Hello Forum,

I am using SW 2014. I am trying to create a flat surface across a hole that I have "Cut" through a thin walled cylinder. It is for a bung connector part that is flat and will be soldered to the flat area of the "hole" in the cylinder wall  when I build this part. Its easy to do for real, in sheet metal, but seems very difficult in SW. I realize the new surface may have to be curved, around its edges to make the transition between flat and the curve of the tube, but I do not know how to model this?

Thanks,

SolidworksSurfacing