I use a method similar to Advent - stand a piece of pipe or tube about 1 & 1/2 or 2'" ID, about 3 foot long, on the garage floor. Stuff a rag in the bottom end of the pipe. Slide inner axle into top end of the pipe until rear of birfield is resting on top of pipe. Now pick up entire pipe/birfield assembly as high as possible and let it drop to floor bottom end first. Usually 5 or less drops will shear thru or deform the C clip, and the axle will drop to the bottom of the pipe, caught by the rag you stuffed there.
Works good for me.
Cheers, Blake