This is indeed not supported, only a single separating character can be used, either by directly specifying the character, or by specifying a unicode code point.
As a workaround, you can either
- Define a custom format (requires writing a plugin); or
- Use the "one record per line" format and then use a preparation recipe to split the lines into columns. You will have to specify the schema manually though (and skip the header line if you have one).