Wanted to share idea
just successfully removed crank with stripped extraction threads
took some hard thinking, worked well

the situation :
DS crank stripped
square taper
loose ball

method :
remove crank securing bolt from DS
remove nds crank with normal extraction process
remove nds cup
remove nds bearings
thread nds cup halfway into shell (no bearings , spindle is floating)
stack spacers around protruding nds taper (socket wrench for ex. used a bbt-22 myself)
thread long bolt into nds taper, head of bolt must bottom against your spacers before running out threads
tighten the bolt into spindle
DS crank bottoms against DS cup, as spindle pulls thru to nds side
stripped DS crank successfully removed