You want all of the background, minus your subject? Fine … select subject and invert it. But you don’t want the sky to be included? Okay, subtract sky. Need to gradually increase (or decrease) the effect on the background (perhaps corresponding with distance), then intersect with the linear gradient. This is easily the most powerful addition Adobe has ever made to Lightroom! Stuff that I used to do in Photoshop I am now doing in Lightroom. It’s not only faster to do it in Lightroom, but it saves me a trip to PS.