target-map considered harmful

So, I've use a lot of MLton cross compilers and have been looking at
how to get MLton packages that achieve this. I was hoping in the
future to be able to type:
  apt-get install mlton mlton-mingw32 mlton-mipsel
... and then get a mlton capable of compiling to my native system,
mingw32, or mipsel targets.

This seems quite easy to achieve, except the annoying target-map file
is one file. Adding the needed sml/basis/config/c/xxx/c-types.sml and
xxx/*.a files in the mlton-mingw32 package is no problem. However, I
can't just overwrite target-map.

Couldn't we instead have a personality file inside the target folders? eg:

cat self/personality
i386 linux
cat i586-mingw32msvc/personality
i386 mingw