So plan B is to use a cheater bar, but also to immobilize the crank arms. Often you are working against the rotation of the crank when removing pedals or the crank arm. It is hard to hold the crank arm still when exerting rotational torque on it. That is another advantage of trying to squeeze the wrench and crank arm in the same hand. There is no rotation of the crank that way that doesn't contribute to getting the bolt out. But if that doesn't work:

What I do is place the bike long ways in a doorway with the DS crank atm placed vertically against the door frame on the side of the frame that acts as a block against the crank rotating when you turn the self-extracting bolt. Then a long torque wrench or a cheater on the small Allen wrench should do the job. Just you or have an assistant hold the bike firm against the door frame, and you should have no trouble getting the bolt loose.

As I mentioned above, this works great for removing stuck pedals too.