Check out Iron Rock Offroad. They make custom bump stop extensions that bolt between your bumpstop cups and the frame. Nice Aluminum units that don't rust. I think they can make any length that you need.
'78 Cherokee Chief: 360/TH400/NOS QT, '04 Grand Cherokee: 4.7/545RFE/242HD w/SYE, JK Rubi front axle, 4.56 gears, Protofab rear bumper/tire carrier