Hi,
I believe you should be able to do this, but you will need to make some modifications to the code in the initialization program for one of the squall line cases (in the dyn_em/module_initialize_ideal.F file). You can use one of the other 3d cases in the file as a template (for e.g., you can use the seabreeze case or b_wave as a guide). Once you are happy with your changes, you will need to recompile the code to incorporate the modifications you've added.