How many light aircraft have the fuel to go somewhere else if they can't get into Norfolk. None of them.
After all, isn't that why they are going there in the first place. Because they can't go anywhere else!!!
No need to carry enough fuel to divert from overhead Norfolk though there's a few lighties that have the endurance to do so. I know of many light aircraft that have transited via Norfolk on their way across the Tasman. It happens to be the closest point along the way from/to NZ.
You make a plan, with a suitable alternate and you have a PNR. Plan A is to pick suitable wx and go to Norfolk. You re check the weather prior to your PNR, if it's all good then continue with plan A, if there's any doubt revert to plan B and return/proceed to your alternate.