The best trick is to stop BEFORE the bolt breaks and get heat and shock sent to the frozen bolt. Also rock the bolt both directions gently. If penetrating oil can get in, it will work wonders. When going back together use a little anti-sieze.
If it were in front of me I would use what I have at my disposal, which is a plasma cutter to gouge out the broken easy out, then hit it with lots of TIG heat, finally welding on a couple of nuts, and of course an impact air hammer with a point bit will break the crud.
FWIW this style of bolt extractors do work very well. I have three different extractor kits for bolts, along with other type of fastener extractors, and have never broken one yet.