It's not an elegant solution, but I soldered a quarter wave wire onto my HC-05 at the base on the antenna and it seemed to help the range/reception quite a bit. I have done this on other cheap 2.4 GHz wifi dongles as well with a significant improvement in performance. You could probably twist together two thin pieces of magnet wire to make a low impedance twisted pair transmission line and then fan these out to make a dipole. I think a lot of the RF design in these cheap dongles may be intentionally poor to limit the range or just poorly done and so any kind of wire like that is an improvement.