Otherwise you will break off two screws about half way down and leave steel bits embedded in the oak frames well out of reach, and then spend the next hour heating each screw with a gas powered soldering iron to soften the epoxy so that you can extract them. You will find that about 20 seconds of blowtorch setting per screw works. When you have use large washers, they act as a heat sink and you will need more.
If you have not used washers, and the screw heads are in the wood, then a traditional electric soldering iron touching the screw will probably work, it will just take longer.
Perviously I had tried the trend grabit and concluded that bronze was too soft and it would not work, but after reading a review where they emphasised "slow speed" as the key to getting it to work, I tried it again after I stripped a haed on a 2" bronze screw which was supposed to hold down a batten. It was still proud about 1/8", like the Grand old Duke of York, neither up nor down.
Sure enough the trend grabit grabbed it and it came out nice and slowly.
Stripping one bronze screw out of 28 x 2" screws into Oak is a reasonable record.
It's all done now. Though I now have a pair of 1" long broken screw bits in my framing and no good way of getting them out. The deck screws broke in half as I started to unscrew them so the bits are about 1" down.