Don't ever say never. A lot if not most of the vineyards around here (Northern Virginia / Central Maryland Area - including other areas in the Mid Atlantic) use Sevin on their vineyards.
Most commercial growers apply with an air blast sprayer so it goes EVERYWHERE. The concentration you used sounds excessive. I still recommend you contact the manufacturer and see what they say. I would still say you can use it (the sevin you mix with water) and spray the top of your canopy with a back pack sprayer.
What kind of grapes are you growing and where do you live? The earliest any grapes are ready for harvest around here are some of the whites and some of them are ready around the 2nd week in September. The reds usually are harvested around the end of September with Merlot being the first. The Cabernet Sauvignon hang until mid to late October. I am saying all this because you may have a variety than can hang longer and thus let nature wash off some of the residue.
There is one other option. You can go ahead and harvest, crush and make your wine and send it out to a lab and have them analyze it for you. They may even be able to tell you in advance what they would recommend without even testing it and charging you. Virginia Tech has a enology program and a lab. You may want to give them a call and state your problem.