DY what would the problem be?
Putting aside the technical details of lifnei iver which probably wopuldnt apply since chalav stam is readily available as are things to carry. Even if it were, or if you want to call it mesayeia. What aveira is there?
Assuming that person is allowed to eat chalav stam/carry on Shabbos. (Obviously if you hold even he cant carry/eat chalav stam that is a sepperate discussion) IT is nto an aveira for that person so what lifnei iver/mesayeha could there be?