I think this is probably a job for the spherical fall-off zones. Try turning them on (if they aren't already) and adjusting the zones to exclude the pig's belly. The inner zone will need to encompass the leg in its entirety, or some bits of it will be left behind. The outer zone can be shrunk until you get the effect you want. I find it helpful to set the element view to wireframe when adjusting fall-off spheres (and magnet zones) - it makes it easier to see the shape of the zone in 3D.