In jEPlus, any files referenced with an "ASSIGN" statement will be scanned for parameter search tags. So you should be able to insert search tags into the b18 file, e.g.

CONSTRUCTION GROUND LAYERS = FLOOR STONE SILENCE CONCRETE INSUL 
THICKNESS= @@thickness@@
ABS-FRONT= 0.8 : ABS-BACK= 0.4

and define the parameter in jEPlus with "{0.005, 0.06, 0.04, 0.24, 0.08}" as the values.