How to implement d3d9.dll override to run my 3D Display?

I'd like to get my autostereoscopic 3D display running with unity. It comes with a d3d9.dll, which alters the way the content is rendered (so the display can handle the real 3D info) and then passes it on to the real d3d9.dll.

So with Crysis for example I just drop the .dll in the root folder, the program loads it and everything works fine. Details can the be adjusted with a config file.

It just won't work with unity. I placed the .dll anywhere in the hirarchy of the exported Windows Player but it just isn't loaded (it will generate a log file when started). I have tried to place it in the plugins folder and export it with the build, no success.

By the way, Unity is using direct x 9, right? Do I have any influence on what version it is using?

Any hint would be appreciated. Thanks, -kiu