I have used high heat and large impacts on the ends of the crank arms before. Both are on the "last resort" list and replacing after is assumed. Simply cutting the LH arm is easier at this point.
Some tricks before you get this desperate is to secure one side's arm along the chain stay with strong strapping (old toe clip strap) doubled or tripled around both then work on the other side's pedal. If you can remove the pedal cage, leaving the axle in the arm, a pipe wrench with extension can be used on the axle. Take care with the exposed chain ring teeth and your hands
Andy