Compiling Rack and plugins with the Visual Studio compiler would be all-or-nothing, because it uses a different ABI from MinGW. So you’d need to compile all the dependencies, and Rack itself, and any plugin used in your patches, using MSVC.
Out of the box that can’t be done, because there is code in Rack that uses GCC extensions that MSVC doesn’t understand, like variable length arrays for instance.
The way plugins refer to the Rack API at runtime is a bit alien to MSVC-compiled DLLs as well - the plugin DLLs refer to symbols in the executable as though it were a DLL, which is the Unix shared object model rather than the Windows DLL model. Some monkeying about to create an import library for Rack.exe would be needed to make that work.