Hi John,
I've looked at how I could hook my build scripts and patches into MXE for native MSVC compilation. I've worked on the MSVC supports tools (compiler wrappers and support libraries) and one sample package (libiconv). I've put the result in attachment: this patch only contains the modifications to the existing files, I didn't include the new files to keep the patch readable.
Could you have a look and let me know whether there are things you're not comfortable with.
Michael.
msvctools-libiconv