You can only run one socket empty if you have an electronic ballast & it has to be wired in parallel. It is prob not worth it to take apart a brand new fixture to do rewiring even if it is possible, so you may as well leave well enough alone.
If you get an actinic bulb for the other side, then you would have only one bulb with light the plants can "see". That would be the easiest solution.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.