Securing Xsporter racks

I've got a set of Thule Xsporter racks with the adapters for my truck and they're great. My only concern is that they'll get stolen at some point when I leave them on. Thule now offers them with a locking mechanism that goes over the adapter mounts, but they don't sell that piece separately. Has anyone found a way to lock them to their truck? I need that peace of mind, these things are expensive.

 

I'm pretty sure you can buy the locks separate. That's how Thule makes so much gawd damn money, they sell EVERYTHING separate.

I had a friend that had this same issue with custom made racks. He found some nut fasteners that used a special tool to tighten and loosen it. Just get stainless steel ones though...

 

OP- did you ever find a solution?