As far as Win32 is concerned, there is very little difference between a .exe and a .dll. If a function in a .exe is exported--they usually aren't but there is not reason why they cannot be--then Win32::API will be able to load and call that function. You just name the .exe inplace of the .dll in the call:

 use Win32::API;
  my $function = Win32::API->new(
      'theExe.exe, 'int foo( int a, int b )',
  );
  $return = $function->Call(3, 2);
[download]

If the .exe in question happened to be the same .exe that is currently running an embedded Perl interpreter, that would work fine too.

Whether this symmetry holds true for other OSs I have no idea.