Writing dynamic dreams requires C++ code and a pretty good understanding of how DirectX works. This includes setting up a scene, manipulating vertexes, sprites & textures and drawing those.
If you are a seasoned developer, you probably know where to look and what to do to get the info needed to write a dynamic dream dll.
If you don't know Direct3D (or C++), you are probably going to have a hard time making anything work anyway, even with a basic SDK.
I understand how not having access to a SDK is, but Stardock is working on it and as Brad said earlier, it's taking time to build something good. Just take a look at the Keyboard Launchpad SDK (yes, there is one

). If Stardock was to release something similar for making Dreams, there would be an outcry!
In the end, it all comes down to how much time you want to invest in it. If you just want to play around with dynamic dreams, you will have to wait for the SDK. Otherwise, most of the info needed is out there, you just have to look a little bit deeper.