i've found the best way to stop an animal from doing something for attention is to totally ignore it. that's how you train a dog not to jump on people when they come in the door - tell everyone who visits to totally ignore him and eventually he realizes that's super boring and he move on to something else. my cats used to howl at the bedroom door in the mornings too, and i did the same thing. the sound drove me crazy, but they learned that howling didn't get me up and pouring food in their bowls. it only took a couple days before they got it.
training to use a bell for attention or something is fine as a distraction, but then you're just going to get him constantly ringing the bell. not as destructive as bar chewing, but still pretty obnoxious and you're still conditioning him that making noise = attention. i say just ignore him. randomly give him treats or pets when he's chilling and being still and quiet. i don't think he's lacking in entertainment, maybe just feeling a little needy and knowing he'll get what he wants when he chews. just make sure he's not going to break his teeth or anything on the bars. he should get the picture quickly though so you shouldn't have to really worry about it that much.
i've found with animals that negative correction like spraying with a bottle doesn't really work that well as they either become afraid of YOU, because you are the one making them uncomfortable, or they realize that they can do what they like as long as you aren't in the room to spray them. that's why people famously are surprised when they find their cats on the counters while they're at work.