Have you tried to study the exercises for the left hand alone by E. R. Blanchet ? they are the 64 preludes of Op.41, they are very difficult and at times cruel, but they soften your left hand a lot and strengthen it tremendously if you study them with constancy and for months with patience. I can attest that they work because I myself study them daily and my fingers have benefited considerably. Of course they are not specific exercises for the Beethoven sonata but they can help to work on the technique of the left hand and prepare it for the kind of passages you mention. Thanks for sharing the exercises you wrote, I've been trying them, they are really excellent! we Best regards!