Oh that will work. I can just see it, "Uhh, could you wait a sec Mr. gun confiscation guy so I can break down my AR-15, insert the bolt carrier, load it and then shoot you"
I am sure that a person in his position will have lots of pre notification when something like that is going to happen, especially if he means to use it.
Additionally, what makes you think it normally “doesn’t” have the bolt? If I knew some people were coming to take a picture of some specialty weapons I had, they would not be where I normally keep them, and they would not necessarily be in the configuration I normally enjoy.
This is the kind of person who probably carries concealed, so i would bet they are not gonna be able to take it.