An off the shelf CVT (comet 20, 30, 40 series etc) could be modified to more appropriately work with an electric motor. This would be done by modifying the driving pulley of the CVT so that it would simply grip the belt in it's relaxed state. The spacing of the pulley halves is determined by a spacer on the shaft, this would need to be ground/turned on a laithe. Likely a little guess/test would yield the best results! Non slipping CVT's are common in industrial applications as opposed to vehicles.