Non-simple answer yes, you can do this. The Mono project doesn't use the .net framework, being a port of .net, and is available for windows. It's main problem is it lags behind .net and the project itself is currently in trouble as the main development team was recently sacked. If it doesn't already support COM access you could implement it yourself.
You could also consider
cross net[
^] which compiles .Net assemblies into ANSI c++.
Another option is for you to write your own c# compiler and re-implement the class libraries already available in the framework. The effort required would be immense, but theoretically possible.
Personally, I'd go with Dalek Dave's answer ;).