You still need the air in the tire, and the fluids change nothing when it comes to pressure.......true, there is less air in the tire, but the exerting pressure on the tire/side wall needs to be the same. As stated - check pressure at 12 o'clock - and place the pressure in the tire that is required for the application you are doing....i.e. - FEL will require more pressure on the front tires, filled or not. A Ballast box would require more pressure on the rears, filled or not.
remember - the "air" in the tire.....is the ONLY shocks you have!