Did this, geez, maybe twenty years ago to a Glock 19 Gen 3. Used a shop heat gun -- not a hair dryer -- to SLOWLY heat up the hump until the back of the hump was soft, NOT the sides. Pressed down and rolled it on a pad made out of a couple of old towels laying on my workbench. Heated it up again and repeated the process until I got the shape I wanted. It ruined the checkering, of course, melting it and smearing it flat. No biggie, I sanded it down and stippled the backstrap. Didn't completely do away with the hump; it's a little more slender than that on a Gen 4.
Wear gloves, for Zeus' sake, and TAKE YOUR TIME. Patience is key. I'd read about a guy who used the candle method and decided the heat gun was a better idea. It was.
Long before that -- in the late 90s? -- I did the Acraglass-fill-in-the-hole-in-the-hump method to a pair of .40 caliber Glocks, an early 23 and a 27 -- Gen 2, maybe? They came out okay, but getting a proper finish was a bear. This was before stippling was a thing, it was so long ago.
I like the Gen 4 models and the Polymer 80 grip style, and I'm a huge fan of the 43, 43X and 48, so I don't do much melting anymore.
Not my picture, but gives you the general idea of what you can do with the heat method. If. You. Dare. lol
Filled in the hollow backstrap, ground it down and used liquid truck bed liner to finish. This is an old picture, I redid it later and it looked much better. Young and dumb, but it worked and it got carried and banged around and did its time for me back then.
Same here, Acraglass in the hollow, some grinding and truck bed liner. Old pic, so yeah, it looked like crap but it felt great in the hand, shot a lot and carried for years.