I think you may not quite accomplish what you are looking for. They will only restore sag below normal loaded height, but won't add much beyond that. Some Cs definitely sit low in the back, but not all do, so you results may very. I can add about 2" clearance to the hitch of my van, but I have long-travel tapered airbags.
If you are willing to spend some big bucks, true air-ride allows for much more air-spring travel, plus a much smother ride. Normally they come with a "kneel" feature, but I suspect it shouldn't be hard hard to add a "climb" setting too.
http://www.stengelbros.net/ReycoGranning_c_33.html