For those interested, I found that Overgrow had previously released a hack (
here) that tackles this issue in a different way--by limiting posts made within a certain timeframe by any unregistered user. His hack is not session specific and instead will prevent any guest from posting within xx seconds of another guest posting. His is more of a hack than a "bug fix."
The modifications I've included here are session specific and extend the floodcheck function to include unregistered users in the same way that registered users are currently checked.
Best wishes,
Paul