Well, your approach is quite interesting. It is not impossible to do it that way and also to have it more or less perspectively right in the distance, however, you will need two, and in case the stairs should not only be used in a 1-square-width corridor, but also in rooms with 2 squares width, four walls to accomplish it. Thus in your screenshots, the stairs should consist of slots A and B from two different walls, meeting in the center of the viewport, instead of slot E from a wall in front of the party. Maybe you already did it that way, I cannot conclude from the screenshot...
I thought about making a huge treehouse earlier, in which a similar kind of stair would be used, however, I dropped that idea because it would be very much graphical effort. With your stairs, it's more or less the same. The player of course will consider it impressive, but it will take days until it is really convincing...
If you still have not totally lost hope of getting somehing like this done, I could try to come up with templates (they are just forming somewhere in my brain). While thinking about it, I realize that to make it absolutely perfect, 8 walls are needed...
My treehouse stairs would have been easier, since with organic looking walls, it is easier to hide minor perspective inconsistencies...
By the way, any progress with the channels? I guess I asked earlier, but I darkly remember you were distracted by other things...