I'm currently in the process of installing a kitchen island with a bar overhang and I came across this thread.
My island is made up of two 36" base cabinets with 4" overhang on each side and a 10" bar overhang on the back. The corners of the bar overhang were cut off at a 45° angle. (See diagram) I chose a 10" overhang because that is what my parents have at their house and it seems comfortable. The counter top will be made up of a 3/4" plywood bottom and 1/2" plywood top glued/screwed together and then covered with 12" porcelain tile. I'm also running into the same problem of adequately supporting the overhang and I want to shy away from using corbels as much as possible. I had planned on using the 1/4" x 2" flat bar method as previously mentioned. I'd use a router to dado the 3/4" plywood and place the bars there. I'd probably purchase 24" long bars that would extend about 8" into the overhang and the remaining length over the cabinet.