metalwork in a bum bag, underneath a baggy jumper.
Trying to hide it would be the worst option. You'll have to take it off to go through the metal detector and they will be suspicious about why you were carrying something in an unusual way.
Bum bag would be good for things you might plausibly need on the flight. As well as hand baggage, you're usually allowed a coat, a camera and a 'personal item' such as a handbag.
First you have to pass security, and the scanner operators don't know who each tray belongs to so don't know or care how much stuff you have and are only interested in checking it's not dangerous. Then you have the gate staff who don't care what it is, only whether the bag is too big or heavy for the overhead locker.
This is how I do it: My last flight was to South America with gear to sail to Antarctica, then go kayak camping. So I had a ski jacket with pockets. Then a cheap kids 5 litre packpack as a personal item, with stuff I might need on the plane, which went under the seat in front. Then a 30 litre Alpkit lightweight backpack as hand baggage, with anything that was valuable, prohibited in hold baggage or hard to replace at the destination. Finally an 80 litre backpack weighing a fraction under 23kg. (It's 20kg on some flights). As Loki says, 23kg is an effort to pick up, and even taxi drivers commented on it. The bags themselves are all minimalist, packed with soft stuff on the outside. You can easily use up 10% of your baggage weight in the bags if you're not careful.