Well, if you can do it with effects, the circle effect alone can get you 90% of the way, you could save it as a preset and just double click it anytime you want, without nothing selected it would create a comp size grey solid and apply. (You already have the Vignette Lightning preset to test it)
But really, how many times a day do you need that? Cause personaly I just do: Crtl + Y, set to black, double click round mask tool, Ctrl + Shift + I, "f" to feather. Its like 10s. Even though I have access to the Sapphire Vignette plugin thats pretty robust, I rarely use it.