Free action, unready shield.
free action, switch grip to two handed
full action, attack
Free action, switch grip to hold weapon in one handed
free action, re equip shield (has on free hand at this point.
sounds fine to be.
Of course, he is forfeiting his two handed attacts of opportunity. Most two handed fighters are not going to be thrilled about that.
also, sounds like a good time to disarm him