I don't think this can be done on the basis that the compilers and resources used by them are not open source / shared by microsoft.
Technically though there's no stopping you using C# as a scripting language in your apps and building with your own compiler ... but why would you?
I'm guessing the idea is that Microsoft handle that for you.
Having said that, maybe if you can figure out what the parts are and programmatically call them you should be able to grab a stream of JIT processed code from there you can put it where you want (in theory of course), but that would mean making unsafe calls in to undocumented assemblies that Microsoft have probably obfusticated just to make life real easy.
Has anyone seen any source for the actual compilers in .Net?
Can't say i have ...
Would make for some interesting tricks though.
HOWEVER ....
In the reflection classes i'm sure you can call "Emit" somewhere that gets the framework to write things like the code for statements / type definitions, maybe there's something in those namespaces that takes the output of Emit and stuffs it in to the compilation process...
What a cool concept !!!