Re-Centering the Camera view after Shift Drag? This seems like something obvious, but I just don't know where to find this.

I'm using blender for projection mapping applications, and have set up my camera to emulate the base position and FOV of my playback environment.

Using Shift+Numpad-Enter to get the view into a 1:1 mode works just fine. My problem is that if I accidentally hold Shift and Middle-click-drag, the camera view frame gets moved within the viewport.

Is there a simple way to reset this back to the center. "Eyeballing" it back to the middle just isn't precise enough for me. I'd rather just be able to hit a keystroke combo and not have to worry about it.
The only option I know of is to select the camera in question and then press Home before repeating Shift+Numpad Enter

Pressing Home with the camera selected runs the 'View All' command and will bring the camera back in view and centred but it will also adjust the zoom so that all the camera is visible, possibly loosing the 1:1 ratio. So it would be necessary to repeat the 1:1 view shortcut afterwards.