Easier method: Clamp the freewheel tool in place using a long bolt, and a big washer. - Won't slip now. If the tool has a wrench fitting, get something like a 24" breaker bar, and just hang off it (cranks clmaped in vice/whatever) If the tool needs a spanner, add the spanner, then find some wide tube to use for more leverage, or try and add the long bar. That's how we done it at work to my one anyway...