As a data point, I phoned in to book a combination of flights once ( AC/BA so not bookable online) and I was clearly taking to a UK call centre. The agent entered the flights I wanted and then gave me a quote in GBP. However, I live in Canada and was originating in Canada, so she realized the error and asked if I'd rather pay in CAD. I said yes, she redid things and came out with the same price, but in CAD.

So it should be possible to pay in a different currency, regardless of the POS.