type
 PCmdArgs = ^TCmdArgs;
 TCmdArgs = array [0..$FF] of PWideChar;

procedure SendArgs(argc: Integer; argv: PCmdArgs);
var
 I, Offset: Integer;
 Buf: PWideChar;
 cds: TCopyDataStruct;
 hMem: THandle;
begin
 if (argc <= 0) then
   Exit;

 Offset := SizeOf(PWideChar) * argc;
 cds.cbData := Offset;

 for I := 0 to argc - 1 do
   Inc(cds.cbData, (lstrlenW(argv[I]) + 1) * SizeOf(WideChar));

 hMem := GlobalAlloc(GHND, cds.cbData);
 if (hMem <> 0) then
 begin
   cds.dwData := 12345;
   //cds.cbData := argc;
   cds.lpData := GlobalLock(hMem);

   for I := 0 to argc - 1 do
   begin
     Buf := PWideChar(Integer(cds.lpData) + Offset);

     lstrcpyW(Buf, argv[I]);

     Inc(Offset, (lstrlenW(argv[I]) + 1) * SizeOf(WideChar));
     PCmdArgs(cds.lpData)^[I] := Buf;
   end;

   SendMessageW(Handle, WM_COPYDATA, 0, Integer(@cds));

   GlobalUnlock(hMem);
   GlobalFree(hMem);
 end;
end;

procedure OnCopyData(pcds: PCopyDataStruct);
var
 Args: PCmdArgs;
begin
 if (pcds^.dwData <> 12345) then
   Exit;

 Args := pcds^.lpData;
 ...
end;

procedure SendArgs(argc: Integer; argv: PCmdArgs);
var
I, Offset: Integer;
Buf: PWideChar;
cds: TCopyDataStruct;
hMem: THandle;
begin
 if (argc <= 0) then
   Exit;

 // Резервируем место под кол-во элементов в массиве + под сами элементы.
 Offset := SizeOf(Integer) + SizeOf(PWideChar) * argc;
 cds.cbData := Offset;

 for I := 0 to argc - 1 do
   Inc(cds.cbData, (lstrlenW(argv[I]) + 1) * SizeOf(WideChar));

 hMem := GlobalAlloc(GHND, cds.cbData);
 if (hMem <> 0) then
 begin
   cds.dwData := 12345;
   cds.lpData := GlobalLock(hMem);

   PInteger(cds.lpData)^ := argc; // Заносим кол-во эл.

   for I := 0 to argc - 1 do
   begin
     Buf := PWideChar(Integer(cds.lpData) + Offset);

     lstrcpyW(Buf, argv[I]);
     PCmdArgs(Integer(cds.lpData) + SizeOf(Integer))^[I] := Buf;

     Inc(Offset, (lstrlenW(argv[I]) + 1) * SizeOf(WideChar));
   end;

   SendMessageW(Handle, WM_COPYDATA, 0, Integer(@cds));

   GlobalUnlock(hMem);
   GlobalFree(hMem);
 end;
end;

procedure OnCopyData(pcds: PCopyDataStruct);
var
 argc, I, Offset: Integer;
 argv: PCmdArgs;
begin
 if (pcds^.dwData <> 12345) then
   Exit;

 argc := PInteger(pcds^.lpData)^; // кол-во эл. в массиве
 argv := PCmdArgs(Integer(pcds^.lpData) + SizeOf(Integer));

 Offset := SizeOf(Integer) + SizeOf(PWideChar) * argc;

 for I := 0 to argc - 1 do // КОСТЫЛЬ, правим указатели
 begin
   argv^[I] := PWideChar(Integer(pcds^.lpData) + Offset);
   Inc(Offset, (lstrlenW(argv[I]) + 1) * SizeOf(WideChar));
 end;
end;

function MakeDrop(const FileNames: array of string): THandle;
var
 I, Size: Integer;
 Data: PDragInfoA;
 P: PChar;
begin
 Size := SizeOf(TDragInfoA) + 1;
 for I := 0 to High(FileNames) do
   Inc(Size, Length(FileNames[I]) + 1);
 Result := GlobalAlloc(GHND or GMEM_SHARE, Size);
 if Result <> 0 then
 begin
   Data := GlobalLock(Result);
   if Data <> nil then
     try
       Data.uSize := SizeOf(TDragInfoA);
       P  := PChar(@Data.grfKeyState) + 4;
       Data.lpFileList := P;
       for I := 0 to High(FileNames) do
       begin
         Size := Length(FileNames[I]);
         Move(Pointer(FileNames[I])^, P^, Size);
         Inc(P, Size + 1);
       end;
     finally
       GlobalUnlock(Result);
     end
   else
   begin
     GlobalFree(Result);
     Result := 0;
   end;
 end;
end;

Drop := MakeDrop([ParamStr(1)]);
if Drop <> 0 then PostMessage(hMainWin, wm_DropFiles, Drop, 0);
GlobalFree(Drop);

procedure DropArgs(hWnd: HWND; argc: Integer; argv: PCmdArgs);
var
 pdf: PDropFiles;
 hMem: THandle;
 I, Offset, Len: Integer;
begin
 if (argc <= 0) then
   Exit;

 Len := 0;
 for I := 0 to argc - 1 do
   Inc(Len, lstrlenW(argv[I]) + 1);

 Inc(Len, Len + SizeOf(WideChar) + SizeOf(TDropFiles));

 hMem := GlobalAlloc(GHND, Len);
 if (hMem <> 0) then
 begin
   pdf := GlobalLock(hMem);
   pdf^.pFiles := SizeOf(TDropFiles);
   pdf^.fWide := True;

   Offset := pdf^.pFiles;
   for I := 0 to argc - 1 do
   begin
     Len := lstrlenW(argv[I]) + 1;
     lstrcpynW(PWideChar(Integer(pdf) + Offset), argv[I], Len);
     Inc(Offset, Len * SizeOf(WideChar));
   end;

   GlobalUnlock(hMem);

   if (not PostMessageW(hWnd, WM_DROPFILES, hMem, 0)) then
     GlobalFree(hMem);
 end;
end;

if Drop <> 0 then PostMessage(hMainWin, wm_DropFiles, Drop, 0);
GlobalFree(Drop);

const
 IDCD_COMMANDLINE = 12345;

procedure SendCmdLine(hWnd: HWND);
var
 cds: TCopyDataStruct;
begin
 cds.dwData := IDCD_COMMANDLINE;
 cds.lpData := GetCommandLineW;
 cds.cbData := (lstrlenW(cds.lpData) + 1) * SizeOf(WideChar);
 SendMessageW(hWnd, WM_COPYDATA, 0, Integer(@cds));
end;

procedure OnCopyData(pcds: PCopyDataStruct); // для примера :)
var
 argc: Integer;
 argv: PCmdArgs;
begin
 if (pcds^.dwData <> IDCD_COMMANDLINE) then
   Exit;

 argv := PCmdArgs(CommandLineToArgvW(pcds^.lpData, argc));