Hmm, so the tiled resources won't run on older dx11 gpus...feelsbad.jpg
you can always try to implement it by yourself.
for example, the first public appearance of mega texture was for DX9 hardware, in enemy territory quake wars (idtech 4 with Opengl 2.1?)..
here is also an "old" (2011) Microsoft DX11 and XNA Math implementation: http://blogs.msdn.com/b/chuckw/archive/2011/10/28/tiledresources11.aspx