If you are afraid of getting bit, put a pair of heavy gloves on, but I would still suggest taking him out to be handled if taming him is important to you. If he's in your collection to mostly be a breeder and you have other skinks who don't mind the "cuddling", then maybe just watch yourself when you put stuff in his tank.
If he is biting inanimate objects just because they're not where he is used to them, then my guess would be that he's grown territorial over his tank. It may not be something you can train him out of --I don't know as I have no experience with this. But my suggestion is to, still, confidently picking him up (hence the gloves if you can't be confident without them) and removing him from the tank. See if he still acts aggressive out of it.
Any skink I've had that's been cranky (I haven't had any aggressive ones, just ones who do not want anything to do with being handled), I always pay attention that their mouth is pointing away from any of my body parts, at least until I get a feel for what makes them nervous and/or what makes them flip out.
Make sure the first grip on him is right behind his head (like I show in one picture in
this thread) so he can't turn around and bite you, and then quickly place your other hand so you pin his back legs --I have found this to be the best way to prevent them "crock-rolling" on you to get away. Once you've grabbed him, make sure to loosen your grip whenever you feel him calming down; open your hands when he's no longer fighting to get away --but make sure you are relatively close to the ground in case he bolts.
Once you know that he's not going to charge everything that moves when he's out of his tank, remove your gloves (if you used them) and handle him with your bare hands. It's easier to keep a safe hold on them without gloves, and you want him to get used to the fact that your hands grabbing him is not a bad thing.
Let us know how it goes.