A while back I went to clean my old pair of Shimano SPD pedals, and accidentally unscrewed (completely) the tension adjuster screw. That screw, screws into a small metal plate that pushes against the ends of the springs (inside the pedal). I had to carefully (with a pair of needlenose pliers) hold the tension plate in place while screwing the tension adjuster screw back into the plate. It was difficult because you had to hold the plate against the tension of the springs until the screw threaded into that plate. It wasn't easy, but it wasn't entirely difficult because my SPD pedals were basically open (they were the mountain style low-end Shimano pedals). Worked great afterwards.

Now, in your case it may be a little more difficult (those pedals seem a lot more closed). But there is most likely a plate that sits at the top of the pedal body (in between the jaws (or whatever they are called)). I had to unscrew mine to be able to give me the clearance needed to get the pliers in there and aligned with the screw.

Hope that helps, and it might take some time, but it should work. Make sure to only work on the one, so you have a reference with the other one.