You'll have to load and unload the DLL yourself then (instead of declaring a function as external)

eg. suppose there is a procedure proc that takes an integer as parameter, you'll have to do
something like this

type
  TProcPtr = function(var iParm : Integer);
var
  MyProcPtr : TProcPtr;
  Handle : THandle;
  Parm : integer;
begin
 Handle := LoadLibrary('YOUR.DLL');
 if Handle <> 0 then
 begin
   @MyProcPtr := GetProcAddress(Handle, 'proc');
   if @MyProcPtr <> nil then begin
     MyProcPtr(Parm);
    {do sth}
   end;
   FreeLibrary(Handle);
 end
 else
    application.messagebox('DLL not found', 'Error', MB_OK);
end;