I was using a CSV reader that would do it based on header names and that worked fine until I thought about the fact that it might say EUR because of my own portfolio.
I then switched to an index-based reader, but that was even more problematic because depending on your date range it might not include all the fields. As discussed here: Common format for history export file (CSV)
So I feel like I need to make something custom which is a mix of both, or do pre-processing where I remove all the currencies within parenthesis.