Air helper springs aren't going to give a vast amount more clearance...a couple inches, maybe, but not enough here IMHO. Approaching from an angle probably won't help here either as there doesn't appear to be enough space to get past the sharp transition before straightening out. The problem isn't the rear axle, per se, but the long overhang in the back combined with the quick transition from flatish street to slopey driveway. The same steepness of driveway with a gentle transition into it would be fine.
Basically, this unfortunately falls into a similar category as "How do I park my 28' motorhome in a space that's 26' long?"--there's no reasonable answer. One can imagine constructing some sort of wheeled dolly that raises the rear wheels several inches above the ground, and then rig up a system to safely pull the motorhome up with a winch or something. Ruben Goldberg would be proud.
