What I did is similar to LGFs additional crank method.
This was on a bike belonging to the husband of a friend of my wife.
It was a Giant Trance X3, 2008 I think, the extractor threads on NDS crank had stripped so crank arm was looking like getting destroyed to remove it to replace knackered BB. So when I saw him at the weekend he asked me what could be done to fix his bike, idiot that I am I said "I'll get it off nae bother". Tried a method that had worked on an old Shimano crank, a ball joint splitter, wouldn't fit due to BB having spacer for arm to hold against. So tried a bearing puller that locks the pulling arms in place but due to steel puller and aluminium crank the puller was just sliding and scratching crank. .
Then I had a bright idea of somehow bolting/fixing another crank arm that had good extractor threads in parallel onto stripped one. Removed pedal then bolted the 2 crank arms together with a spacer between pedal threads so that BB ends of cranks were in line and square to each other. Rummaged in shed and found a 2" diameter exhaust clamp, fitted this with the u-bolt part around the back of stuck crank with a big socket in hollow in the back of crank to prevent damage from the u-bolt, the other part of clamp, the pressed steel bit, just clamped up against the "extractor" crank. Tightened it all up, it wasn't moving. Had to cut down a longer bolt to about 40mm to fit inside the bolt threads on BB so that the extractor could reach being too far out from the BB axle.
So the moment of truth arrived, tightened extractor and the 2 cranks were no longer tight together, did the clamp nuts up tighter but then noticed that the cut down bolt in BB had crumpled with pressure. Replaced it with slightly thicker bolt which didn't bend as much, gave the crank arm a bit of a tap with tool number 1 and off it came. Apart from scratches which are merely cosmetic and a wee dent from big hammer the crank is OK and can go back on with new BB.
For future use I'll find a proper high tensile steel bolt that will thread into BB axle to sort the bending of the spacer bolt made of cheese I had to hand.
