No.
And why not?
Just use middletexture for the door + backside texture.
If you create an ordinary polyobject, you don't need backside texture, because it consists of one-sided lines... on such a polyobject you can use middle texture but to no avail.
Look:
This is a good example for that. (Doom in UDMF)
There are two ways to create polyobjects: the first is with startline, in this case you don't have to create the polyobject as a sector, so it consist of one-sided lines.
The second way is with explicit lines, in this case you have to create the poly as a sector but it should be the same subsector as its holding sector.
Your third method is not a usual or conventional way to do it.
