Create native Unity3D plug-in (for OS X and Windows standalone)

My Unity3D game must to be able to compress and decompress speech using the open source Opus codec ([login to view URL]). As you will see, this code builds easily into static and dynamic libraries from command-line tools, but I need to be able to call into them from my standalone Unity game instances (OS X and Windows are required... Linux is extra credit). A head-start to creating the glue needed may possibly be gleaned from this wrapper project: https://opusdotnetinvoke.codeplex.com. I'd like to have greater control over sampling rates than specified there -- offering 11025 and 22050 in addition to those provided in an enum there, and ideally allowing sample rate to be passed as an integer. I will provide a simple test scene in Unity3D to verify functionality. An acceptable implementation must include source code and build trees by which I can reproduce your working implementation using open source build tools where possible, and Visual Studio and XCode where necessary.