The switching process can be disrupting depending on how it works, I agree. But even so far as to include grabbing a spare monitor "you never actually look at" or spoofing one? For that, I admit I can't see why just using one of the inputs on the monitor you already have isn't an option.
Unless of course the monitor doesn't have additional inputs (but it was never specified the hypothetical monitor is ancient) or they are all already used (again wasn't specified).