cutting torch.
This is truly a bad idea. The heat from the torch can destroy the heat treating in the triple and even boil the oil in the front forks due to the heat transfer.
I would opt for a Sawzall.........................
Okay my honest solution would be to try Craftsman extractors. Should that not work you may need to find someone to weld another nut to the existing nut. As scary that may sound I know a welder or two good enough to pull it off.