Assuming his posek is working within the framework of Orthodox Judaism, yet holds of the Eruv. Why cant that person carry?
The point isn’t whether that person can carry, the point is whether the person who holds the eruv is passul can help him to carry.
Can I tell a Sefardi where to buy Kitniyos he plans to eat on Pesach?
I don’t think that’s the same, because it’s based on minhag.