It has been a long time for me on pressure plates, and I don't remember the need to do this, but here a couple of ideas.  So don't take this as only opinion, just how I would go about this topic if I did not have any instructions.  Before starting, I would weigh a dry plate and then after saturating weigh a wet plate, to see how much water is involved.  If the pressure plates have a tubing release of water when under pressure, put the plate under water and pull a vacuum on the tubing to pull water in.  It should expedite the saturation process.  If you leave the pump running, make sure to put an intermediate container that can collect water so the pump is not damaged.  The other option is to put the plate in a pressure cooker of similar, add ample water and add compressed air pressure to the air release to force the water in.  I am not sure this would work if the air from within the pressure plate cannot be released in some way.  Perhaps drilling a hole in the pressure cooker  for the pressure plate drain tubing to release air may help, and then when you see water coming out, it must be saturated.  I don't know that either would work, but if you have a dry weight and a wet saturated weight of the ceramic plate, that would serve as a future check. 

In addition, an internet search may help understand there imay be specifics with any analysis to address to get to the data quality you want to present.

http://downloads.geo-slope.com/geostudioresources/examples/7/Pressure%20plate%20drying%20and%20wetting.pdf

https://www.soilvision.com/downloads/docs/pdf/research/GeoTest_V32N5_2009_Lins_Schanz_Fredlund.pdf

 Thanks William , for finding out these resources.