I cannibalized the soft loop and small piece of kydex (that I covered in Velcro to be held on place by the BFG belt loop) from an old holster. Shoot Tom (Orionz06) from Dark Star Gear a message. I've had a few people asking about loops to do this mod, and I've been bugging him to offer little loop kits to do so.
As a little more detail why I went this route, the soft pouch keeps it really comfortable to carry. A rigid AIWB holster has to be pretty precisely placed to be comfortable. Being soft, there's a little more leeway for placement. Carrying vertical, particularly with a single soft loop, helps minimize the amount of belt space, which is good cause I carry a lot of stuff. It could be carried anywhere, not just AIWB, but I like being able to access it with either hand.