It is possible to link the .mat files to the PLECS Look-Up tables (from the Control domain). Please see the attached example. I have attached both PLECS Standalone and PLECS Blockset models.
For example, if test.mat is the name of your .mat file,
In PLECS Standalone, we load the .mat file by entering load('test.mat') in the Model initialization commands window, which can be accessed from the PLECS menu bar of your model: Simulation > Simulation parameters > Initialization.
In PLECS Blockset, we load the .mat file by entering test in the InitFcn window, which can be accessed from the Simulink menu bar of your model: File > Model Properties > Callbacks.
Then, on the PLECS schematic, you can simply enter the variables defined in the .mat file as the inputs of your look-up table.