Ok, thanks for clarifying your position. I was hoping that I didn't waste a lot of time arguing against something that wasn't there and thankfully I wasn't. So here we go.
Concerning this point, I have pointed out were Thomas explicitly says that God is omnipresent in Part1, Q8, A3 he says:
Therefore, God is in all things by His power, inasmuch as all things are subject to His power; He is by His presence in all things, as all things are bare and open to His eyes; He is in all things by His essence, inasmuch as He is present to all as the cause of their being.
Well you are right concerning God's transcendence. But you only look at a partial of what Thomas commented on how He is present in all things here is what Thomas wrote in P1, Q8, A3, which is an expansion from his comment I quoted above:
I answer that, God is said to be in a thing in two ways; in one way after the manner of an efficient cause; and thus He is in all things created by Him; in another way he is in things as the object of operation is in the operator; and this is proper to the operations of the soul, according as the thing known is in the one who knows; and the thing desired in the one desiring. In this second way Godis especially in the rational creature which knows and loves Him actually or habitually. And because the rational creature possesses this prerogative by grace, as will be shown later (12). He is said to be thus in the saints by grace.
But how He is in other things created by Him, may be considered from human affairs. A king, for example, is said to be in the whole kingdom by his power, although he is not everywhere present. Again a thing is said to be by its presence in other things which are subject to its inspection; as things in a house are said to be present to anyone, who nevertheless may not be in substance in every part of the house. Lastly, a thing is said to be by way of substance or essence in that place in which its substance may be. Now there were some (the Manichees) who said that spiritual and incorporeal things were subject to the divine power; but that visible and corporeal things were subject to the power of a contrary principle. Therefore against these it is necessary to say that God is in all things by His power.
But others, though they believed that all things were subject to the divine power, still did not allow that divine providence extended to these inferior bodies, and in the person of these it is said, "He walketh about the poles of the heavens; and He doth not consider our things [Vulgate: 'He doth not consider . . . and He walketh,' etc.]" (Job 22:14). Against these it is necessary to say that God is in all things by His presence.
Further, others said that, although all things are subject to God's providence, still all things are not immediately created by God; but that He immediately created the first creatures, and these created the others. Against these it is necessary to say that He is in all things by His essence.
So you are only referring to Thomas' comment about God being present in all things by His power, but Thomas expands on this and states that God is also present in all things, by His presence essence.
So yes Thomas teaches Omnipresence.
You are right concerning God cannot have a "real relation" to creation; but you are missing the point that the creature has, must have a "real relation" to God. In this Thomas writes in P1,Q28,A1:
Reply to Objection 3. As the creature proceeds from God in diversity of nature, God is outside the order of the whole creation, nor does any relation to the creature arise from His nature; for He does not produce the creature by necessity of His nature, but by His intellect and will, as is above explained (14, 3 and 4; 19, 8). Therefore there is no real relation in God to the creature; whereas in creatures there is a real relation to God; because creatures are contained under the divine order, and their very nature entails dependence on God. On the other hand, the divine processions are in one and the same nature. Hence no parallel exists.
I really have no idea how you can get to the point of claiming Thomas did not teach God's omnipresence when he wrote a whole question, with four articles on the matter, claiming otherwise.