It doesn't appear this is an option, but perhaps this workaround will do the trick for you. Put the entire text of the script into a variable at the beginning of the script. First line could be something like
script_text = Load Text File( "Path\script.jsl" );
Then, whenever you want to tell the user what line is executing,
//marker001
Write( "The script has now progressed to line number ", Contains( Words( script_text, "\!N" ), "//marker001" ) + 1 );
Just make sure "//marker###" is the only text on its line.