If people all over the world can send you an email that doesn't make you omnipresent, it just makes you reachable.
If you believe that heaven is organized in such a way that its human inhabitants are unable to see or be aware of anything that happens on Earth, then you are correct that intercessory prayer is futile; but I don't see how you can justify that belief. it does not follow from "omnipresence is an attribute of God alone", that the "presence" of a saint in heaven is so limited that no information from Earth can become known to the saint. You don't have to be aware of every place at every time in order to be aware of a single person in a particular place at a particular time.
And as Peter was coming in, Cornelius met him, and fell down at his feet, and worshipped [him].
Now the word worship is comgin from is "proskuneo" which means kneeling or prostration to do homage (to one) or make obeisance, whether in order to express respect or to make supplication