Could you enable the cat and hook up the required sensors but keep the one after where the cat should be out in a plastic bag zip tied on the frame rail to read clean if they say it's reading to clean then ask for a green sticker for being good for the environment but try to hide it the best you can don't leave it in plain sight. That way you don't have to put a cat on

 

If you have visual checks like we do here in SJ, I think you have no choice but to reinstall everything. They opened my hood to look for missing parts and also looked under the truck to ensure the 'pieces' are all there...

Readiness tests take about 100miles of varying driving conditions and at least a couple cold-start drive cycles to clear if I remember right..