I would just kneel; the occasion is too great for me to do otherwise. At my age kneeling is no biggie whether there is a kneeler or not. We are however permitted to stand if the floor or the ground is not suitable for kneeling. Standing posture is perhaps older than the kneeling. Pews and kneelers admittedly were more of a recent innovation.
There is no standard posture while we kneel (or for that matter stand). Common school of thought is to gaze at the Lord and say in our heart “my Lord and my God”, remembering that Thomas needed to see the Lord’s side and hands in order to believe. We are all not worthy but made worthy by him but it is reasonable to utter the words that Thomas said because this is really the Lord.
As the Blood is elevated we are to say in our heart, “thank you Lord”. Thanking the Lord for the blood shed on the cross for the expiation of our sin.
It is an awesome moment; if we are tongue tied and unable to think of anything, do not worry. People are struck dead when they came face to face with the Lord; we are no difference. Just be there transfixed at the awesome wonder of God. Peter jumped from the boat and swam away from Jesus, the minute he realized the awesome reality that Jesus was God and understood that he being a sinner was not worthy to be in God’s presence. Some people react differently; so I think there is no hard and fast rule on what we should do during the consecration.