Hi Guys,
I had done this in the past, I used a "sketched bend" drawn corner to corner set the angle to maybe 10 dgrees. Then readjust your existing side bends to 80 degrees.
The actual application I did was a 3 sided pan that had 2 sketched bends that initiated in the corners and went to the middle of the side with out a flange. Dont start the line in the exxact corner, back off maybe .10 each direction, and dont end exactley midpint, back those off from each other as well.
Hope this helps,
Ken