Just copy/clone to package directory of OpenWrt SDK. Run 'make' to build with package defaults or 'make menuconfig' to select build options, and then 'make' to build it. Sugestions, improvements are welcomed. Have Fun.
Keep in mind that a real device may require a set of modules to operate which might are not selected together automatically. Do not forget to select all of them by hand. You can use linuxtv.org's wiki to determinate what components are used by your device or use desktop Linux to see what modules are loaded when the device is inserted.
Building with only SDK is supported at the moment. Sorry. This is because only SDK provides stable kernel configuration. Without it we could introduce unending "dependency hell" or failed compilations.