How to set boundary conditions from parametric solver

hello,

We want to successivly run a DC_model by changing only some boundary conditions (i.e. current density on a face) on only some geometric objects (i.e. electrods).
We want to use parametric solver to perform this operation. For that:
We tried to group together boundaries in Options/Boundary Expressions and linked them to a variable. This variable was defined in Options/Constant as a value of current density. In the menu Solve/parametric sweep, we typed in the window "parametric name" the group name of the boundaries we want to change value. In the window "parametric value" we typed the constant name which represents the value of current density.
But it doesn't work! help!!

Thanks for your help