[JThiessen]

DOT approvals are a freakin joke IMHO. You can put whatever GVWR on the side of your rig and they will certify them with no logical engineering look at the actual specs of the vehicle. The only time they actually step forward with a voice of authority is when there is a pending lawsuit on something. Sore subject for me...
Yes, a mechanical devise would likely be a better approach, and much easier to accomplish. Can you clamp around the rim of the wheels somehow, without damaging them? I'd almost have to think there should be a commercially available device that one could copy in some fashion.