finite plane wall

I understand that using command
fix xwalls1 all wall/gran model hertz tangential history primitive type 2 xplane 0.0
can create a infinite X-plane wall at x=0.

Could anyone tell me how to create a finite plane wall? For example, a wall from (0, 0) to (0, 2) in 2D or in 3D formed by 4 points.
Or it can only be done by importing mesh file?

Thanks!

Jason