Javascript: callback after event reported?

Is there a way to get a callback from Raven that runs when an event is reported (so just after Raven.lastEventId() is populated)?

I can see that Raven’s _sendProcessedPayload method supports a callback, however _send never populates that parameter

I’d like to build a feedback request that appears unobtrusively at the bottom of the screen (that, when clicked, calls Raven.showReportDialog(); to show the User Feedback modal).