Ah, I see what you mean now. Preact will treat any "properties" as extra properties on the event. example

    _lnq.push(['_logEvent', 
        {
            name: 'added signature', // event name
            external_identifier: "12345", // id of the target item referenced
            note: 'agreement.pdf', // human-readable label about this event
        }, { 
           // extra custom parameters for this event
           signature_mode: 'draw'
        }
    ]);

We do need an example of this on our docs. I'll add that. Thanks!