Quote: "I mean - Do you think there is a way you maybe use DirectX and GDK together (and independantly) to acheive the effect you're after?"
Sure, once you have a pointer to D3D device, you can do anything. So technically - Yes. Practically - No, because the DGDK graphics engine is useless then. You do need the control over rendering order if you want to squeeze some speed out of the machine.
Regarding the FastSync - the documentation says that it only omits processing of Windows messages, so not a big gain.
Anyway, to get back to the original post - it's still possible to set two textures to a model and use a single pass shader which combines both textures at once. This can not supply every effect, but in most cases it should do the trick (and is even faster than multiple rendering!).