Case and LCD Removal
The Canon Elph 450 weighs over 5 oz fully assembled.
The case can be removed, it splits into to main halves and a wrist strap attachment. Small screws hold it on the camera.
The LCD screen can be removed while allowing the camera to continue functioning. There is a single screw hold it on and two ribbon cables. The shorter ribbon cable is straight forward, while the second wider cable goes through a hole in the camera body and is plugged in on the opposite side. It may be difficult to reattach those ribbon cables.
The lcd screen is not yet removed in this picture. The ribbon cable just to the lower left of the lense is connected to the lcd screen.
The camera weighs about 2.9 oz after all that, and 3.6 oz including a battery.
Plastic around the ribbon cable can be removed, exposing the switch that takes pictures.
Control
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To bypass the mechanical button, short two of the legs of the push-button switch together for half a second or so.
One of the two ends of the push button (with arrows in picture) is at 3.3V and the other appears to be floating. It's possible that just connecting the floating side to an external 3.3V source (ref to same ground) will take a picture.
One thing we don't want to do is tie either end of the push-button to adjacent cameras. If any of the cameras is powered off or fails then all of the cameras will be unable to take pictures- we confirmed this on the test bench.
The battery ground and the grounding 'planes' around the body of the camera are the same (0 ohms resistance between them).
What we ended up doing was using the trigger circuit to short the camera buttons once every 7 seconds. Diodes between the cameras kept crosstalk and interference down, and allowed the cameras to function if one died.
Field of View
The horizontal field of view of the Elph 450 is about 54 degrees. For a decent panorama we should have adjacent cameras overlap by a 2-4 degrees. With four cameras we can easily get a 180 degree panorama.