I used the bike-brake leaver approach for my one camera, very portable scanner. Some pics are below, and the build thread with more pics and a video of the scanner in operation, is here:
http://www.diybookscanner.org/forum/vie ... =14&t=3007
Some notes about the hardware around the camera.
a) The main frame is a simple 5" L bracket available from hardware stores.
b) The lever is a 6" carriage bolt which has a hole drilled in it for the brake cable. The two wing nuts grip the cable (actually only one is needed to press the cable against the hole -- which is what bikes do, but I used 2 to make sure it doesn't slip). I use wing nuts so I can quickly disassemble/assemble the scanner without tools because it is a knock down scanner, as shown in the last pic at the build thread above.
Another hole was drilled in the L bracket as close to the right position as possible (a little high to be safe) for the 6" carriage bolt so that it would be positioned right above the camera at the right distance from it for the grommet to it's job.
c) The rubber grommet is what presses the shutter release.
d) In the "rest" position the leaver of course keep the grommet and the shutter release away from each other and the tension created by the flexing lever bolt and L bracket when the brake leaver is pulled is what creates the spring action to return the lever back to "reset" position when the brake leaver is released. You can see this flex/spring effect in the video in the main build thread.
e) A standard barrel adjuster used on bike brakes is attached to the L bracket and the cable comes through it, just as it would on a bike near the brake pads.
f) My Olympus has it's tripod connector at the left of the camera (near the corner in the L bracket) and all the nuts on the bolt down there allow easy adjustment of the camera position relative to the the lever and grommet. I use a carriage bolt, but ideally an allen bolt (with no head) would be better so it's easy to remove the camera from the bracket by opening just one wing-nut.
g) The problem with the Olympus having the tripod socket at one end is that the camera flexes down as the grommet presses on the shutter release. That's why the middle bolt -- which attaches the bracket to the ball socket via a female-female extension nut -- is up against the camera, to give it support and stop the flex.
The L bracket has 3 holes on each side, which are not on the centre line of the bracket, so the camera is a little off square when positioned on the bracket so that it rests on the centre bolt and the lever bolt is also in the right place. You can see the off-centre holes and the what it does in some of the pics in the main build thread at the link above.
Cameras with the tripod socket in the middle would need an additional hole drilled for a support bolt to stop them from flexing. Alternatively the camera can be mounted against the L bracket but then the lever would need to be adjustable to position it in the right place or the grommet replaced with something adjustable to press the shutter release. Larger cameras will need a 6" L bracket and perhaps a longer carriage bolt lever (or piece of threaded rod).
As seen in the video at the link above, the set-up works flawlessly except for one minor detail. Because the Olympus tripod socket is at one edge, the weight of the camera tends to force it to swivel around the tripod socket and it's the direction that unscrews so if the camera is not held fairly tightly it can "flop" down -- which is handy when you want to change the battery or get the memory card out but not otherwise! I tried to increase the friction on the centre support bolt by adding a bit of rubber between it and the camera, but then the flex returns when the grommet presses the shutter release. However if the camera is held tightly -- but not so tight to strip tripod the socket joint loose -- I've used it for hours on end without any problems. But I recently realised I could use the camera strap, which is on that far side, near the camera buttons, as a support cable to hold that end of the camera up by wrapping it around the ball joint's hand nut and that's solved the issue completely.