First and foremost, make it buyable with ce. Charge 5K ce per expansion pack if you have to, so that it will be cheaper to trade for it. At least think about doing this. Another solution to this, would be to facilitate buying the DLC. Making some kind of interface to where you could offer CE for a piece of DLC would be nice. Then, whenever someone went to buy the CE, if the CE offered for DLC was greater than what they would have gotten anyway..., that would be automatically paid for and sent to the CE buyer.

An idea of how facilitating it would work-

Person one wants DLC and has CE
person two wants CE, and has money
Person one puts up a bid of x ce on the mission's expansion
Person two buys ce, just like normal, and receives person one's ce that they have offered, which may be worth more than their purchase their trying to make.
person one gets a DLC

Or at least make an item that when used grants access- like a 'crimson hammer pass', that you could trade and sell on auction house. That would help the financial situation as well.

The actual levels were nice, however I'd like to see some of the recons and mortars spawn in the clockworks, and I'd be quite happy to use either of their weapons myself... perhaps as some kind of future weapon?