Ok. I kinda get what you want. They make something called a flu bracket. Ive only seen them up to 5". You go to a Risidential sheet metal shop and ask if the have A Flu Bracket and draft stop(piece of sheet metal with a hole in it) that is the size you want(4,5,6,7,8"). They will ask why you need one bigger than 5" if you ask. Be prepared and tell em your venting a kitchen hood and the inspector is a dick and wants a bracket. Why you dont know.lol... If they have what you want take it home put draft stop in attic over your hole. Then Screw the flu bracket to it(use small 1/4 sheet metal screws. Dont push to hard and dont wind your drill out. You drilling threw metal and into sheet rock. Sheet rock suck especially when you let the screw spin in it. Put pipe as I described before into flu bracket and tighten the bracket. Flu Brackets have a 1/4" nut and flat tip combo nut. I think flex duct with an expensive metal tape sealing the hole is easier, faster, and less of a pain in the ass but your the one there that can see what you want. This is the only way to suspend a pipe like you want. All the other ways I know are rig jobs. I looked for a pic online but couldnt find one. Sorry. I think when you see the Bracket and draft stop you will get how it works.