I was afraid it might take a local contact (your immigration lawyer).

In Portugal AIUI, it takes either a physical visit to a bank office yourself - bring ALL of the documents you might conceivably need and someone who speaks the language well just in case - or someone acting as your "financial representative" to the same end. There are companies that specialize in the NIF / bank account part of the process. I cannot speak to other EU countries and only have my own very limited experience with Novobanco to go from, though.

One thing I learned from reading the "Americans & Friends PT" FB group recommended by, IIRC, Rubic earlier in the group, is that the outcome can vary wildly depending on what branch you go to, what individual you talk to, how well you explain yourself. Some people report being told by someone at a particular bank branch that they absolutely were not accepting new American clients, period, while others report having no problems setting up an account at the same bank (maybe a different branch) in the same week. I gather such experiences are the norm in PT :-)

Regarding Santander, the visa application requires you have a Portuguese bank with a specified minimum balance. I doubt Santander would work (but presumably if you're applying to Spain, it would be fine there).