Personally I'd use Biroudo. I think most Portuguese borrow words were assimilated long ago and the now original writting/word should be just part of the etymology.
Ex. 切支丹 = Kirishitan/christian in ancient Japan, as opposed to クリスチャン = christian in modern times.
Another (reverse) example (?)
Recent borrowed words aren't quite assimilated the same way so we should always write them in the original language.
But then again, whoever named the tracks most likely just wanted to be cool using the kanji instead of ベルベット so whatever.