A few things come to mind, the special pipe wrench for getting at faucets from the underside. Some of them can do internal gripping as well, and may be small enough.
There are also internal pipe wrenches but they might be a bit hard to find.
And there are also some rather large screw extractors out there, both the spiral kind and the splined kind which won't wedge the threads as badly.
I'd check a local industrial tool supplier to see if they have them, or if you know a place that repairs heavy equipment or manufacturing machinery they may have it. At the hydraulic place I worked we had all of the above and removing something like that would have been a fun change of pace job that I might have been able to do for little or no charge. It's a nice ego boost to get out a part that "nobody has been able to remove" even if the tool is really what makes the difference.
Steve Birmingham Lowell, Massachusetts USA
Message: 9 Date: Wed, 28 Oct 2009 01:46:36 -0400 From: <Carb7008@cs.com> Subject: [CR] Broken Fixed-Cup Removal at SBK To: <classicrendezvous@bikelist.org> Message-ID: <d50.5c223c75.381934bc@cs.com> Content-Type: text/plain; charset="US-ASCII"
Here in Sacramento we have a volunteer bike-biz catering to folks. A gentleman came-in tonight with a loose crank,which upon removal of BB, the fixed cup had circumferentially broken in-two such that about 3/4" of the inner portion of cup remained threaded in the shell about 1/4" deep. Every effort to remove, including un-screwing, cutting with hacksaw, notching with file, prying with screwdriver, failed to remove hardened (why do you think they call them "fixed"?) race.
I doubt a cold chisel, which we didn't have, would have cut-through. A Dremel tool may have worked if we could have gotten the cutting-wheel inside
the BB shell. Needless to say, the gentleman walked his OT bike home. Any ideas short of torch or liquid nitrogen embrittlement?