Both of the two vendors for body lifts include bumper relocation brackets to solve that problem. It's part of why the kits are more expensive than some folks hope for. In other platforms, body lift kits are cheaper.
For our platform, you can get away cheaper with a suspension spacer lift, and since that sort of lift actually gives you more frame-to-ground clearance, it's much more functional. Doing a body lift alone is sort of silly, unless you're looking for a lift meant for appearance only. In which case only a few people will see the purpose.