GNAT subunit naming

Hi.

We have these files:

-- hello.ads
package hello_device is
  procedure func1;
  procedure func2;
  procedure func3;
end;

-- hello.adb
package body hello_device is
  procedure func1 is separate;
  procedure func2 is separate;
  procedure func3 is separate;
end;

-- hello_f1.adb
with ada.text_io;

separate(hello_device)

procedure func1 is
begin
  ada.text_io.put("func1");
  ada.text_io.new_line;
end func1;

-- hello_f2.adb
with ada.text_io;

separate(hello_device)

procedure func2 is
begin
  ada.text_io.put("func2");
  ada.text_io.new_line;
end func2;

-- hello_f3.adb
with ada.text_io;

separate(hello_device)

procedure func3 is
begin
  ada.text_io.put("func3");
  ada.text_io.new_line;
end func3;

Now, I can tell GNAT that the files hello.ads and hello.adb
provide the package 'hello_device' just fine with a
couple of Source_File_Name pragmas but I can't seem to
work out how to tell GNAT that hello_f[123].adb provide
the subunits of this package.

Any help would be appreciated.