I have seen people fed the with the left hand. The still use the thumb, but they do not grasp the rifle on the left side, they reach over, and grasp the rifle on the right side. It sounds weird, but the feeding was flat and smooth.
I never tried it, as I sold my SKS a while after that, and did not shoot it during that period.
Dunno, might help. I never feed bullets well with the strippers and my right hand.
Behold a pale horse, and the man that sat on him was Death, and Hell followed with him