If you're going to break the firearm down like that you may as well just put it in the trunk....with magazine unloaded due to a local ordinance. Better to carry a revolver in that situation (with a speed clip which is not a magazine). Still can't be concealed in the passenger compartment but can be carried there in the open.
Another Option, get a Black Powder pistol. They are NOT "handguns" in Oregon, they are "firearms". They can be concealed within the vehicle without a CHL.....though you still can not have them "loaded". However, a BP pistol is only loaded if it has a powder charge, ball, AND primer. Just leave the primers out. Then again, I don't have one so I don't know if it's more time consuming to prime the cylinders on a BP pistol as compared to loading a semi auto magazine or using a speed loader clip with a revolver. AND I guarantee if you do have an encounter with police they'll NOT know the damn law.