I haven't tried this with bikes, but it's worked well with car bits, hence I'd advise caution but...
assuming it's a metal washer, I'd heat the whole caboodle up in the oven till it gets nice and toasty (10-15 minutes) then take it out and allow it to cool. the lower volume of the washer will allow it to cool (however contract minutely) faster than the rest of the crank, which should loosen it sufficiently to allow you to prise it out. it may take a couple of attempts, and no doubt some ridicule, but a sound theory in my opinion...
I haven't tried this with bikes, but it's worked well with car bits, hence I'd advise caution but...
assuming it's a metal washer, I'd heat the whole caboodle up in the oven till it gets nice and toasty (10-15 minutes) then take it out and allow it to cool. the lower volume of the washer will allow it to cool (however contract minutely) faster than the rest of the crank, which should loosen it sufficiently to allow you to prise it out. it may take a couple of attempts, and no doubt some ridicule, but a sound theory in my opinion...