Umm I have an idea. What if you had two accounts, and gave your other accounts your GS. You then somehow got your account locked/banned. Locking your account isn't that hard just have a bunch of people log on and recover it back.
Then just send in the appeal to get the account to get unlocked and unbanned and if it gets accepted maybe the item will be duped.
I just thought about this when reading the thread, it would be hard to ban but I think locking and unlocking your account is pretty simple.
Someone try this and tell me if it works, because I just made it up off the top of my head.
If you get your account locked, your account still exists and the item can still go to your bank. You just cannot log onto your account.
I don't think you will find a dupe because when you lend out an item the person recieving it does not get the item. They get a totally different item with the same name, same bonuses, same examine info and same animation. The item will have different attributes to it. This is an example for the sake if you still do not understand what I mean, when Jagex makes an item lets just say they have these columns for each item.
So example.
This is the original
---------------
Item #9998
Name:Bandos Godsword
Bonuses
Slash:444
Poke:444
Lick:444
Whatever:444
Tradeble: Yes
Extra-
Option 4 <Dismantle>
Add item #4353, #9444 inventory
Examine: A powerful sword ra
----------------
This is the copy
---------------
Item #10233
Name:Bandos Godsword
Bonuses
Slash:444
Poke:444
Lick:444
Whatever:444
Tradeble: No
Extra-
Option 4 <Dismantle>
<msg>You cannot dismantle this, it is not your property!
Examine: A powerful sword ra
----------------
So they basically get an item just like the Bandos Godsword, but it isn't.
Thats why when you get lent a godsword it even has a little circle in the middle of it just to signify it's lent or that the hilt is welded onto the blade.
Anyway so every item that you lend out I'm sure jagex made an exact copy of it with limitations so they checked each items attributes.
So the people that say they dismantled the lent godswords, I'm sorry but that is false. I even tried it as soon as it came out

my friend was like what the heck is this red circle in the middle of the godsword, I was like what?...