Kneeling is more than custom. It is scriptural.
_Oh come let us worship and bow down; let us kneel before the LORD our maker” (Psalm 95:6). _
Wherefore God also hath highly exalted him, and given him a name which is above every name: That at the name of Jesus every knee should bow, of things in heaven, and things in earth, and things under the earth; And that every tongue should confess that Jesus Christ is Lord, to the glory of God the Father. - Philippians 2:9-11
And worshipping the the Eucharist (Christ Himself) is idolatry? Really?
Now, kneeling is not required, but many Lutherans do. Lutheran pastors are not mandated to genuflect, but some do. But to say that worshipping Christ and His real presence is idolatry strikes me as hyper-anti-Catholic.
From the website linked below, on the topic, a quote from a prayer book published by CPH:
Now, here we are not saying that one should not worship our dear Lord Jesus Christ in this Sacrament, being present, of that one should not hold this Sacrament with all honor and reverence. On the contrary, since these divine, almighty, true words are believed, all of this follows of itself, and not only in external gestures but also both externally and, first and foremost, in the heart, spirit, and truth. On account of this, such adoration of Christ is not thereby cancelled, but much rather, confirmed. For where the Word is rightly seen, considered and believed, the adoration of the Sacrament will happen of itself. For whoever believes that Christ’s body and blood are there (as there is plenty of evidence so to believe, and it is necessary so to believe), he cannot, to be sure, deny his reverence to the body and blood of Christ without sin. For I must confess that Christ is there when His body and blood are there. His words do not lie to me, and He is not separate from His body and blood." - George von Anhalt, TDP, February 3, pp. 1179-80