Well, I would try this. Nice slow wide approach to the slip head on so you are headed straight into it. About 1/3 in, reverse thrust to back the boat out of the slip to port. Then forward, putting the boat right about where # 4 is on your 3rd pic. Then, just back it in as you would under your backup plan. I think this might give you more positive control throughout the procedure. Backing a long distance can get difficult with wind and if you get too close to shore and try to adjust a little forward, you're going to go to port and closer to shore, alongside that parking lot.