GB - I admire your creativity. But that sounds dangerous as hell. I feel Mark has the best answer. However, not everyone has a few hundred dollars to invest in a good GPS device for their bike. And, we know there are lots of places GPS won't work properly. So IMO, Mark's solution is contingent on two factors that aren't always available.
Backing up the bike for up to a dozen yards or even longer works for me. Like most of us, I have encountered a few instances when I passed a split by too much to back up. Every time I have done this over the last 3 decades, it was due to traffic and safety concerns. What we do can be dangerous. Safety must always come first.
Winston's way seems fine for longer screw-ups. Still, it seems to me that the best way is to ride back to the last known accurate point, get off the road, take a few minutes to carefully re-calculate the remaining splits, and start measuring at that point.
Since I started using Kevin Lucas's handlebar-mounted counter along with my list of splits open in front of me in my rig, I have all but eliminated blowing past a split count.