Sorry, but I think you are asking for trouble or a serious accident. By lowering your receiver, you would be changing the dynamics of your hitch design. A properly designed receiver hitch doesn't carry the weight on it's own, but transfers it to the frame of your tow vehicle. Moving how and where it attaches would change that and you would be setting yourself up for hitch failure IMO.
Grade 8 (automotive grade) bolts are the strongest readily available bolts and they wouldn't hold up to the additional stress you would be subjecting them to - I've used them to repair my recliner at home and they've snapped off, more than once! (poor recliner design, I only weigh 200lbs
Your correct plan of action would be to get either a drop hitch of the right height, or an adjustable hitch that slides into your reciever. They are widely available.