Can you stack the $800 switcher offer with the offers from Costco?

I have a line on T-Mobile that is currently on an installment plan that I am trying to switch over to AT&T. From what I see online, it looks like AT&T will pay off up to $800 for each line I transfer over.

But I am wondering if it's possible to stack any of the offers at Costco with this as well or is that not allowed?