Force line series on second y axis

When I add multiple series’s to the same line plot I have no way to force a specific series to the second axis. There’s one option “Use a split y-axis when necessary” but it leaves it up to metabase whether or not to put the second series on another axis. This is a little bit of an issue because each series I’m plotting is a different unit type (grams vs. pounds) and it doesn’t make much sense to use the same axis for both.