I think unless you have a vice or big visegrips your current method of attack is the best. you'll just have to cut it off. the problem is that this has twisted and is likely out of round so it may be cross threading on its way out.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk