I learned about the slide operation on edges. I use it to select a border edge loop, press gg and then hold alt to slide and increase the size of the border faces. Now I'd like to use this while extruding, rather than moving the edges. I want to keep the original edges and faces, but get a new row of faces along the selected border edge loop. The new border edge loop would be the result of sliding as usual, only the old loop is still there.
Note I don't want to slide the border edge loop to be in the new position and then have to recreate a new loop at the old position.
For example the following shape, viewed head-on orthographically.
Say I want to extrude the selected edges by sliding them. Extruding and immediately scaling is no good: (e, escape, s)
Instead I want to extrude along the lines also used for sliding: (gg, hold alt)
However I want to keep the old edges too. I want to add a new row of faces, the same as when extruding, but the shape of those faces is determined the same way as when sliding.
I hope I make myself clear. I think this question is asking the exact same, however they did not get a correct answer.