How to fulfill if no user input / make input optional

I have a couple benefits that have to do with user names. I have input for those benefits currently, i.e. What's your user name on a particular platform, but for my 1st couple subscribers I already knew it and fulfilled it without their input. How do I mark as fulfilled?

Or, as an alternative, can I make their input optional? One reward I have will use their default gamewisp ID, unless otherwise specified (putting them on a list of subscribers). If they don't respond with a different name, how do I fulfill it? Again, it is waiting for input.