What effect are you going for? If it’s opacity, you’ll need the white ink. If it’s backlit, there are backlit profiles from HP that should work.
However, you can bump up the ink levels in your rip software (if your rip allows you to do so). But the most effective way to do what you’re asking is to run the job twice on the same material. It’s not the easiest thing on hybrids, and you will definitely need adhesion promoter on plexi.