With a little luck and a little work. The luck would be getting the parts. I'd call Antec and ask them to sell you a 3.5" driver case(that's what they call it in their parts diagram. I suspect they mean drive cage) and the 3.5" support bracket.
After you get the parts, it would be a matter of pop riveting the support bracket in place and then attaching the 'driver case'. I don't think the operation would be too hard. If you look at your 3.5" slideout drive cage, you will see how simple it looks to rivet in another support bracket.
The only question is whether you would still have space left for one case fan or if you would lose both. Optionally, you could pare down the size of the second drive cage with a hacksaw or similar tool. It almost looks too simple, which means that it will probably turn into the case mod from hell that will cost you four weekends to complete. lol