I've been thinking about this too since I have the Tone (RIP) hitch and need to lock my bike carrier on occassion. I don't have the rear skid plate (yet) and I still don't have enough room for a locking pin setup.

I think that the solution I have decided on is to install my bike rack and then drill another set of holes further away from the rear of the VX for the locking pin. I will still use the Thule threaded pin in the rear and the new locking pin closer to the collar. I don't think that this will cause any issues with the strength of the hitch or the bike rack.

Just a thought.