I dont think you will have any issue with park staff. Most lakes have a few extra sites that are set aside exactly for this reason. Areas in the  northwest of the park, Manitou, North Tea, Kiosk we have found to be the windiest by far. You may have to plan to be in the water at first light or slightly before, making the most of what calm water you can find.

I would go ahead and plan tnat longer trip, it will be great. The wardens wont be an issue, just give yourself some flexibility for being windbound. Its always a possibility.

Moonman.

I think just about everyone has a story about at some point having to camp off their reserved route due to wind delays or other mishaps. In fact it's fairly common when planning a long trip to work in layover days (a day without moving sites) to account for delays -- in other words to give yourself an opportunity to catch up with your itinerary if things don't go well, which inherently means you're camping off route before the catch-up day. When that happens, just do your best not to take the last site on an at-capacity lake. If you're worried that you may have done so, try to ask passing canoeists if they're looking for a site on the lake.

Now that the interior reservation system is available online, it's easier to make sure you're not screwing anyone over. You can figure out which lakes have extra sites, by looking at how many reservations a lake takes on CAMIS and comparing that to the actual number of sites on a map. You can also see which lakes are well below capacity in terms of reservations on the eve of your trip. If you can remember where a few lakes along your route stand on those two questions, you'll have good candidates for emergency stops. I think the farther you go into the backcountry the more likely there is to be vacancy on the lake, since canoe traffic decreases with distance from access points while campsite density stays roughly the same.

I can't speak much for the summer months but I have been windbound plenty of times in early spring and late fall when out on solo trips. Its nice at this time of year because the park traffic is drastically lower then in July and August so I have never had an issue with finding a site or taking one from someone else as there has always been open sites where I have stayed.

As DanPM stated, just ask canoeists passing if they are in fact looking for a site and worse comes to worse you have to share for a night, but atleast everyone is safe. This usually isn't as much of an issue with wind as if you aren't traveling most likely they won't be either, but with regards to mishaps with gear/injuries it could be more likely.

I don't think any sane warden would give you guff if the situation is explained. I worry more about inconveniencing others as opposed to fines as Im anyone tripping in the park for a while has inevitably come to lake where they had a site booked yet there are no sites available. This happened to me last spring and caused me to have to travel in the dark to the next lake...not fun.