To put it simply: This will never work. You have zero chance of trading an in-game item (or, indeed, items) for an out of game (or meta-game) one. They exist on different "planes" of value.
I'll explain. This was a concept Gary Gygax was particularly interested in due to it's effect on RPGs. He called it the bread-gold-souls trade economy breakup. Bread was worthwhile for other bread, gold was only worthwhile for other gold and souls were only worthwhile for other souls. This is due to the fact that, simply, it's impossible to trade bread for gold (because gold is worth so much more) or gold for souls (again, because souls are worth so much more / gold is unable to be traded for souls at all). (There is a solution for this and that is to allow people to extract "souls" from bread and gold and to make gold bread, but that's getting off the topic.)
Now, in Fable 3, we're currently suffering a complete market collapse in terms of gold AND in-game items due to duping bugs and how easy it is to gain both. This means that the value for in-game items is TINY. I mean, truly minimal even within the game itself.
Compare that with the pre-order DLC meta-game codes. They are worth actual money and quite a good deal of it. They have actual value.
So, essentially, the value of 999,999,999 gold (or any item in game) in Fable 3 is $0.01 whilst the value of the pre-order DLC codes is around $30. There is no way for you to be able to trade enough to make up for the value of the pre-order DLC code.
There is a negating factor in this, and that is fully upgraded legendary weapons. This is due to the fact that they require time and effort (which costs money, technically) but due to duping, they are unlikely to be worth anything at all.
TL;DR: NO ONE WILL TRADE YOUR IN-GAME ITEMS FOR THEIR DLC CODES OKAY?
I'll explain. This was a concept Gary Gygax was particularly interested in due to it's effect on RPGs. He called it the bread-gold-souls trade economy breakup. Bread was worthwhile for other bread, gold was only worthwhile for other gold and souls were only worthwhile for other souls. This is due to the fact that, simply, it's impossible to trade bread for gold (because gold is worth so much more) or gold for souls (again, because souls are worth so much more / gold is unable to be traded for souls at all). (There is a solution for this and that is to allow people to extract "souls" from bread and gold and to make gold bread, but that's getting off the topic.)
Now, in Fable 3, we're currently suffering a complete market collapse in terms of gold AND in-game items due to duping bugs and how easy it is to gain both. This means that the value for in-game items is TINY. I mean, truly minimal even within the game itself.
Compare that with the pre-order DLC meta-game codes. They are worth actual money and quite a good deal of it. They have actual value.
So, essentially, the value of 999,999,999 gold (or any item in game) in Fable 3 is $0.01 whilst the value of the pre-order DLC codes is around $30. There is no way for you to be able to trade enough to make up for the value of the pre-order DLC code.
There is a negating factor in this, and that is fully upgraded legendary weapons. This is due to the fact that they require time and effort (which costs money, technically) but due to duping, they are unlikely to be worth anything at all.
TL;DR: NO ONE WILL TRADE YOUR IN-GAME ITEMS FOR THEIR DLC CODES OKAY?