Yes, that should work. You will have to plug in one of the PLA2, push the Sync button on the side for 3 seconds, release and you will see one of the lights begin to flash. Plug the second unit in and push the sync button for 3 seconds and you will see the lights flash for a few seconds. The middle and right light will then stay solid on both units, showing that they are synced. Now push the sync button on the second unit for 3 seconds and you will see the light flash again. Plug in the third unit and push the sync button for 3 seconds and release. You will see the same lights light up and stay solid on the third unit now. They are now all synced.
You just need to make sure that they are all being used on the same circuit or they will not sync.