Possible to have empty productions?

I have two modes: One where I do a full parse and another where I just want to parse out certain productions. Is this possible? Do I need to setup the Lexer differently or can I handle it in the Parser? If so, for either, any hints would be helpful.

Would love to know this as well. I need to make a production that represents a list of arguments. Like this:

arg_ : arg arg_
arg_ : "empty"