I haven't tested this, but logic tells me that even without such a monitor, you should be able to create and draw to a 10/10/10/2 render target, then draw that as a regular fullscreen quad to any format backbuffer.
D3D9 has a SetDialogBoxMode call, which is not in itself relevant to this discussion, but does interestingly note the following restriction:
The application specified a back buffer format compatible with GDI, in other words, one of D3DFMT_X1R5G5B5, D3DFMT_R5G6B5, or D3DFMT_X8R8G8B8.
This is enough to tell you that support for such modes doesn't exist in GDI.
Mention of GDI is relevant here because it highlights the fact that D3D9 is old technology that is no longer being updated, so you shouldn't expect it to have good support for newer hardware features.
Finally, it's important to note that it's not D3D that draws to your monitor; it's your graphics card. D3D just gives your program a way of telling your graphics card what to draw, your graphics card does the actual drawing. So this is really a problem for the hardware vendors to solve.