Xbox support question

[Myria]

I want to add Xbox as a supported target.  I want the Xbox mode of binutils 
to function exactly the same as "i686-pc-mingw32", with the following 
changes:

1. Subsystem type is defaulted to 14 (IMAGE_SUBSYSTEM_XBOX in ~2002+ 
Microsoft header winnt.h)
2. Default PE base address for subsystem xbox is 0x00020000.
3. Default entry point for subsystem xbox is mainCRTStartup.

(Conversion from ld's EXE output to the Xbox's native XBE format is 
straightforward and is handled by an external tool.  It just would be nice 
to use that subsystem number for recognition, and that base address so we 
don't have to do relocation, since binutils stupidly refuses to make a 
relocatable EXE.)

What is the easiest way I can add xbox as a target?  It seems like I would 
have to clone a lot of the mingw32 code in binutils for the Xbox case.

Thanks,

Melissa