Dll distribution of Conditionally Compiled project

I have a Unity plugin which involves conditionally compiled code for iOS and other platforms, and would like to distribute it as a DLL on the asset store to reduce project clutter.

The basic idea of compiling code to a dll makes perfect sense, but what is the correct way to go about creating and organizing dll assemblies for different platforms that can perform bidirectional communication?

http://docs.unity3d.com/Documentation/Manual/UsingDLL.html

http://angryant.com/2011/02/02/assembling-and-assimilating/